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The semi-arid central Karoo of South Africa is an important livestock farming region, oftentimes characterized by water scarcity and limited grazing resources. This paper builds on previous research that has predominantly focused on post 19th century Karoo rainfall characteristics. The paper aims to: 1) establish the long-term frequency and longevity of droughts or dry periods; 2) explore spatial hydroclimatic variability across the Karoo during given dry/drought periods; 3) compare the timing and duration of 19th century Karoo droughts with those of neighboring regions to the east (Lesotho) and north (southern Kalahari); 4) establish the possible role of the El Niño Southern Oscillation (ENSO) in drought occurrence across the Karoo-Kalahari-Lesotho region; 5) determine whether the so called 'global drought' of 1877-78 is evident in the central Karoo; and 6) place 19th century droughts in a 20th– 21st century context (or visa versa) for the Karoo. Documentary sources were accessed, photographed and digitized from a variety of repositories (Libraries, Museums, and online sites such as READEX). Multi-station instrumental rainfall records (1861–2022) were made available by the Rubidge family at Wellwood farm. Historical droughts (1861–2022) in the Karoo were spatially highly variable in severity. However, severe droughts in the Karoo have decreased in frequency and amplitude (rainfall deficit) between 1861 and the present. • Historical droughts in the Karoo were at times highly variable in space and time. • Long and severe droughts have decreased in frequency and amplitude. • The 1877-78 drought was the most hydrologically severe 2-year drought. [ABSTRACT FROM AUTHOR]

Abstract This paper explores an original approach in which greenhouse gas (GHG) emissions and carbon (C) accumulation are assessed monthly and at landscape scale to account for the highly seasonal monsoon climate and the mobility of pastoral herds that characterize West African pastoral ecosystems. The study was conducted in northern Senegal, in the service area of the Widou Thiengoly borehole, a circular zone of 706 km2 centered on the borehole. The C balance was calculated using an ecosystem approach, i.e. taking all main sources of GHG emissions and C sinks of the ecosystem, not only anthropogenic sources, into account. The annual C balance of the pastoral ecosystem was −0.04 ± 0.01 tC-eq.ha−1.year−1, showing that total GHG emissions were mitigated by C accumulation in trees, soil and livestock. The C balance varied considerably with the seasons, with a positive monthly balance in the wet season, from July to October (+0.58 tC-eq.ha−1.month−1) and a negative monthly balance in the cold dry season from November to February and the hot dry season from March to June (−0.57 and −0.05 tC-eq.ha−1.month−1 respectively). Care should be taken when generalizing these results, which were obtained in a dry year, because of strong inter-annual variations in rainfall. Highlights • Sahelian rangeland ecosystems have a neutral carbon balance. • Accumulation of carbon and greenhouse gas emissions vary strongly between seasons. • The main source of greenhouse gas emissions is livestock. • The main carbon sinks are trees and soils. • Seasonality is explained by both rainfall patterns and pastoral practices. [ABSTRACT FROM AUTHOR]

Abstract: To date, the interpretation of remote sensing images has not revealed wide-spread degradation of the vegetation in the Sahel. However, the interpretation of spectral information depends on a range of assumptions regarding the dynamics of the Sahelian vegetation as a function of rainfall variability and human management. Recent papers have presented diverging views on the vegetation dynamics of the Sahel and how these can be analysed with remote sensing images. We present a further analysis of the vegetation dynamics of semi-arid rangelands, in particular the Sahel, and the subsequent implications for the interpretation of remote sensing images. Specifically, the ecological processes driving the response of the Sahelian vegetation to rainfall variation are re-examined, and a regression analysis of NPP versus rainfall data is carried out. It is shown that the relation between the interannual variation in NPP and rainfall in the Sahel is non-linear and that this relation differs between sites with different average annual rainfall. It has been common practise in remote sensing studies for the Sahel to aggregate data from various Sahelian sites in order to obtain an average relation between rainfall, NPP and Rain Use Efficiency, and to assume these relations to be linear. This paper shows that this approach may lead to a bias in the interpretation of remote sensing images and that further work is required to clarify if wide-spread ecosystem degradation has occurred in the Sahel. [Copyright &y& Elsevier]

Land-use changes have contributed to an increased interest in understanding the drivers of forest regeneration in human-modified landscapes. This is particularly true for arid ecosystems, in which regeneration is relatively less known, but more sensitive to land-use intensification and climate change. This paper aims to identify the relative contribution of seed rain and soil seed banks for the regeneration of the Caatinga dry forest in northeastern Brazil as well as their drivers. We monitored seed rain and soil seed bank of woody plant species during a 14-month period across 15 regenerating (4–70 yr old) and 5 old-growth forest stands. Stand age, precipitation, chronic anthropogenic disturbance, and forest aboveground biomass were our explanatory variables. A total of 5081 seeds from 61 species were recorded in the seed rain across all forest stands (1.81 intact seeds per m2 per month). Regenerating and old-growth stands did not differ relative to average seed rain scores, with the proportion of zoochoric seeds positively associated with forest biomass. In the seed bank, we recorded a total of 5660 seeds from 64 species (5.05 intact seeds per m2 per month), with no differences among stands, except for species richness; with mean seed size positively associated with stand age. Collectively, seed rain and seed bank captured only 40% of the woody regional flora, mostly dry-fruited species (70% of all species). Moreover, assemblages were dominated by a few hyper-abundant species. Our results suggest that the Caatinga dry forest supports relatively low-density and impoverished seed rain and soil seed bank. Additionally, seed rain and soil seed bank do not exhibit directional changes through forest regeneration for most of the attributes, and deviate little from the scores of old-growth forest stands. Compared to resprouting, they may pose limited influence on woody plant recruitment and dry forest regeneration across human-modified landscapes. In this context, Caatinga restoration approaches based on natural seed rain and soil seed banks may be of limited effectiveness. • Seed assemblages in the Caatinga regenerating forests are impoverished and low dense. • Impoverished seed assemblages are linked to low productivity and human disturbances. • Seed assemblages are not affected by forest age, exhibiting little successional trends. • Seed rain and seed bank may play a minor role in the Caatinga forest regeneration. [ABSTRACT FROM AUTHOR]

A large karst area of South-Eastern Italy (Puglia) is characterized by endorheic basins, whose runoff does not discharge into the sea but converges toward internal lowlands and infiltrates or flows into underground cave systems through swallow holes. In such environment whenever intense rainfall events cover large areas and rainfall intensity exceeds the discharge capacity of sinks and swallow holes, significant volumes of runoff are produced and stored on surface causing floods and risks for people and goods. Most of these sinks are often at the end of small independent basins delimited by weak divides and, whenever water storage exceeds the overflow threshold, runoff contributes to downstream areas and, in cascade, large areas may contribute to deepest lowlands. The observation of historical flood events suggests that in such areas traditional methods for the individuation of the design flood event, and in particular of critical rainfall duration, lack of applicability and the worst rainfall condition, for a fixed return time, should be searched accounting for soil hydraulic behaviour and groundwater dynamics. In this paper a rationale for the evaluation of the critical rainfall event and of the flood-prone area for given return period is proposed. A case study is presented showing that for high return period events a “multiple-reservoirs” mechanism is activated that affects the critical rainfall condition as well as the flood extent in the urban areas. [ABSTRACT FROM AUTHOR]

Abstract: In many parts of the world the boundaries between grassland and shrubland biomes have changed substantially over the course of the last century. Many are projected to shift further from being grass-dominated to shrub-dominated by 2050 under global climate change and land use change projections. This paper used long-term surveys and repeat photography to assess vegetation change at the shrubland-grassland ecotone in semi-arid, South Africa. Changes in several climate variables as well as in the cover of grasses and dwarf shrubs over three time periods (1962, 1989 and 2009) were investigated at eight localities within a broad 500 km ecotone between the Grassland and Nama-karoo biomes. Results showed that for most sites grass cover has increased and that dwarf shrub cover has decreased over time. This contradicts earlier views which warned against the expansion of dwarf shrublands in response to over-grazing as well as more recent views which suggest that more mesic biomes in the Karoo Midlands will contract in response to climate-induced aridification. The decline in stocking densities and more conservation-friendly land management practices together with an increase in large wet events in the Nama-karoo biome may have contributed to the increase in grass cover. [Copyright &y& Elsevier]

Abstract: Mediterranean environments are typical of semi-arid regions, dominated by episodes of torrential rain in which the critical variable is not the total rainfall, but the intensity. This paper studies the maximum rainfall intensities at different observation time scales, from 5 min to 24 h, over eastern Spain from 1994 to 2007. The statistical rainfall characteristics for each time scale are analysed and the effects of specific geographical factors – altitude, aspect and distance to the sea – for each observation interval are tested. The results show that extreme intensities are heavily dependent on the time scale. There are two important turning points in this trend, at 1 h and 6 h. With regard to the influence of geographical factors, distance from the sea is particularly important as it is significant for almost all observation time scales. Altitude is only significant between time scales of 30 min and 6 h. Aspect is not significant. Two intensity patterns are also observed: the first includes the highest intensities, at altitudes from 200 to 400 m and at locations 20–30 km from the sea, while the second is related to lower intensities, higher altitudes (900–1000 m) and longer distances to the sea (90–100 km). [Copyright &y& Elsevier]

Abstract: This paper reviews the nature of moisture at Gobabeb, Namibia with emphasis on rainfall, and fog. It introduces the observational record produced by the Gobabeb Training and Research Centre and examines nature and cause of the rainfall record from October 1st 1962 to May 30th 2011. Over this period of 17749 days only 381 rainy days produced a total of 1213 mm of rain with an annual average of 25 mm. 2011 has been the wettest year on record also featuring the two most wettest days (March 12th and May the 6th). 1992 has been the driest year with no rain at all. Over the last 3 decades (1979–2009) the number of decadal rain days has decreased from 77 to 56 to 54 days, while total decadal rain amount has increased from 130 mm to 149 mm up to 300 mm. 193 Individual rain events between 1979 and 2009 were linked to synoptic conditions present in the region including the Zaire Air Boundary (ZAB), Tropical Temperate Troughs (TTT), the Angola Low, temperate cold fronts and cut-off lows (850 hgt geopotential height). Cluster analyses in the form of Self Organising Maps (SOMs), suggests that all synoptic states have the potential to produce rain but that the Angolan low dominates with an increase in TTT activity being evident. Fog collection techniques have evolved through time and suggest a range of possible event types, including advected fog, coastal stratus cloud, high stratus cloud, radiation fog and fog drizzle. While each of these has their own meso- and micro-scale synoptic control and may even vary in their bulk and isotopic chemistry, they collectively make a significant moisture contribution to the flora and fauna of the Namib. Additional sources of moisture are gaining appreciation and include the widespread occurrence of hypersaline springs on the Namib gravel plains as well as micro-scale moisture including vapour in desert soils and regolith. [Copyright &y& Elsevier]

Abstract: This paper presents characteristics of droughts simulated by global climate models (GCMs) under enhanced greenhouse gases conditions. We used a drought index called the Reconnaissance Drought Index (RDI) which takes both rainfall and potential evapotranspiration into account to investigate variations of droughts among 12 regions in Australia. The RDI was applied to simulated climate variables from 14 GCMs performed for the IPCC 4th Assessment Report. The results show a general increase in drought areal extent and/or frequency for most regions. However, the increases are not significant over the North West, North Queensland, Queensland East Coast and Central Queensland. For most regions, the change beyond 2030 is larger than that prior to 2030, but the uncertainty in the projections also increases with time. By 2030, there is a likely (>66% probability) risk of twice or more drought affected area and/or twice as often drought frequency over South West Western Australia. By 2050, this will include the Murray-Darling Basin, South Australia and Victoria, and by 2070 this will extend to New South Wales and Tasmania. For North Queensland such a risk is unlikely (<33% probability) for the next 100 years. This information can be considered indicative in long-term planning focussing on sustainability. [Copyright &y& Elsevier]

Abstract: Many researchers have used time-series analysis of remotely sensed images to gain understanding of the dynamics of loss of vegetation cover in drylands. However, complex interactions between vegetation and climate still mask the potential of remote sensing signals to detect human-induced loss of vegetation cover. This paper presents mixed-effect modelling method for time-series NDVI-rainfall relationship to account for the complex interaction between vegetation and climate. Mixed-effects method is a form of statistical modelling that can simultaneously model environmental relationships for a population and for different groups within the population. In this study, it was used to model the NDVI-rainfall relationship in Somalia and for different vegetation types in the country. Its time-series application removed the interaction between vegetation and rainfall and identified areas experiencing human-induced loss of vegetation cover in the country. On average, it gave an accurate relationship between rainfall and NDVI (r 2 >60%) and detected areas with human-induced loss of vegetation cover (kappa=75%). Although the potential of mixed-effects was shown using vegetation types, other factors such as soil types and land use can also be included in the method to improve accuracy of time-series NDVI images in detecting human-induced loss of vegetation cover in the drylands. [Copyright &y& Elsevier]

Abstract: This paper explores the existence and potential causes of a stationary spatial anomaly, or pattern incoherence, in the seasonal distribution of warm season rainfall in western Mexico. The anomaly is evident in maps of the Month of Maximum Precipitation (MMP) variability over northwest Mexico (NWMx). Instead of occurring progressively as latitude increases, the MMP occurs in July in the southern part of western Mexico and along the main axis of the Sierra Madre Occidental (SMO) to the north, and in August in the central portion of the region, in Nayarit, Durango and Zacatecas. The Month of Maximum Streamflow (MMQ) occurs in a similar spatial pattern but shifts one month later. This feature is explored through inspection of the daily rainfall climatology of the region for stations with more than 20 years of data between 1940 and 2004. We hypothesize that this anomalous pattern in rainfall (and subsequent streamflow) is likely influenced by the complex thermodynamic interaction between the orography of the SMO and the regional monsoon circulation. The possibility that the canyon system known as the San Pedro Mezquital helps drive the anomalous increase of rainfall in August across latitudes limited to of Nayarit is explored. The correlation between rains that fall over watersheds on the western slope of the SMO and rainfall over the Mexican Plateau is also discussed. We also explore the relationship of the rainfall anomaly to the seasonal march of the Western Hemisphere Warm Pool (WHWP) and near shore Sea Surface Temperature (SST) variations as they may impact the land–sea thermal contrast. The results of this study based on daily rainfall and streamflow climatologies suggest that a region exists in Nayarit where atmosphere–ocean–land surface interactions lead to a relative phase-shift in the maximum precipitation and streamflow. [Copyright &y& Elsevier]

Abstract: Temporal variation of aboveground net primary production (ANPP) of arid ecosystems has been associated with precipitation regimes with different results. The objective of this paper was to characterize the relationship between interannual variation of annual and seasonal Normalized Difference Vegetation Index (NDVI), as a surrogate for ANPP, and precipitation in the steppes of Northern Patagonia. In 11 sites encompassing a wide range of conditions and vegetation physiognomies, we studied a 20-year monthly data set of NDVI and precipitation. We took into account the precipitation of current, as well as previous periods of variable length. Interannual variation of annual NDVI was little correlated with annual precipitation, either current or previous. In contrast, it was highly and widely correlated with precipitation accumulated during a few months of the previous growing season. Interannual variation of seasonal NDVI was little correlated with current seasonal precipitation. In contrast, it was significantly correlated with precipitation accumulated during previous periods of variable length according to the season and site under consideration. NDVI was more tightly coupled with precipitation in drier ecosystems. Lags of response between NDVI and precipitation provide an opportunity for forecasting ANPP and suggest even longer lags between climatic variation and herbivore performance. [Copyright &y& Elsevier]

Abstract: This paper provides a brief introduction to the physical environment of Namaqualand as well as an overview of patterns of plant diversity. The diverse array of parent material and geological processes that have shaped the region since the break up of Gondwanaland have created a complex, and sometimes dynamic physical environment, that is partly responsible for the patterns and processes observed in the biota today. The contemporary climate is characterised by relatively reliable, albeit low (50–250mmpa), winter rainfall (>60% winter precipitation) arriving between May and September. East of the central mountains, tropical thunderstorms penetrate the region in late summer (February–April). The presence of the cold Atlantic Ocean in the west not only moderates temperatures throughout Namaqualand (mean max summer temperature <30°C), but also provides alternative sources of moisture in the form of coastal fog and heavy dew experienced in winter months. Recent analyses show that the flora of the Succulent Karoo is part of the Cape Floral Kingdom, now termed the Greater Cape Floral Kingdom. It is one of only two desert regions recognised as a global biodiversity hot-spot and contains an estimated 6356 plant species in 168 families and 1002 genera. Namaqualand, which comprises about one quarter of the area of the Succulent Karoo, contains about 3500 species in 135 families and 724 genera, with about 25% of this flora endemic to Namaqualand. This remarkable diversity, however, is not distributed evenly throughout the region, but is concentrated in many local centres of endemism usually associated either with quartzite mountain complexes or lag-gravel plains (quartz-patches). A major exception to the general pattern of centres of diversity is the true Fynbos vegetation of the highest Kamiesberg peaks where rainfall exceeds 400mm pa. Suggested determinants of the region''s exceptional floral diversity include the complex physical environment, a unique past and present climate and the region''s diverse fauna, most notably insects. The challenge for the current inhabitants and scientists working in the region is to develop a better understanding of this ecosystem so that they will be equipped to deal with the challenges posed by the demands for land and the prospect of global climate change. [Copyright &y& Elsevier]

Abstract: This paper describes and compares the hydrological responses of runoff, soil moisture and groundwater levels to rainfall events for two small semi-arid catchments over a 2-year period. Romwe received 1430 and 756mm of rainfall in the 19999/00 and 2000/01 season, respectively. Mutangi received 756 and 615mm of rainfall in the same years. Romwe generated 520 and 102mm of runoff in the 19999/00 and 2000/01 seasons, respectively, while Mutangi generated 82 and 69mm of runoff in the same years. The runoff response of the catchments was dominated by a relatively quick response to rainfall and with little or no significant contribution from regional groundwater or ‘old water’ sources. Total soil moisture storage to a depth of 120cm was higher at Romwe than Mutangi for the entire study period reflecting the differences in the soil types. The groundwater level was closer to the surface and responded more quickly to rainfall at Romwe compared to Mutangi where water levels were between 12 and 16m below the surface. There was a significant relationship between profile soil moisture and water table level at Romwe and none was observed at all in Mutangi. Significant (p<0.05) monthly rainfall runoff relationships were observed at both Romwe and Mutangi. At Romwe and Mutangi 91% and 76% of the runoff variation was accounted for by rainfall in the 1999/00 season, respectively. The rainfall–runoff relationship were different at Romwe for the two seasons, it was higher in the 1999/00 season than the 2000/01 season when 91% and 49% of the runoff variation was due to rainfall, respectively. The relationships were almost similar at Mutangi during the two seasons. [Copyright &y& Elsevier]

Abstract: Even though drought is difficult to define precisely, rainfall is the most widely used indicator of drought. This paper presents a methodology on modeling of the agricultural drought duration. For this purpose, study area was divided into four hydrologic homogeneous sections as W, CN, CS and E. To constitute the monthly time series of each section, the number of days in each month in which daily rainfall was less than the water consumption of the critical crop was assumed to be drought periods. Then, constituted monthly time series of drought durations of each hydrologic homogeneous section was simulated using ARIMA model. No linear trend was observed for the time series except that of the CS section. In general, the predicted data from the selected best models for the time series of each section represents the actual data of that section. [Copyright &y& Elsevier]

This paper investigated changes in economically important woody vegetation resources around seven settlements located along an aridity gradient in the Kalahari. Available data at different rainfall levels were analysed for different vegetation aspects. Total woody plant density and number of species at each site increased with increasing rainfall level, while individual species density differed at each site irrespective of rainfall, due to other factors, for example, land use as indicated by high stump densities around old and high population settlements. Drought resulted in high mortality of certain species, increasing availability of fuelwood resource in the form of dead wood. However, prolonged drought from climatic changes could result in browse shortage, a vital resource in the Kalahari. There was generally low wood resource availability throughout the studied gradient, without any distinct relation to rainfall, reflecting the influence of other factors such as soils, land use and natural variability. [Copyright &y& Elsevier]

Climate change will likely impact rainfall characteristics in particular locations; the amount, seasonality, variability and spatial patterns. In developing countries, this presents challenges for rural smallholder farmers as their livelihoods are largely based on rain-fed practices. Changes in climate patterns could increase farmers' vulnerability and the need for intervention. In this paper, we develop new metrics of analysis motivated by qualitative research with smallholder farmers. Previous research found that farmers' understanding of historical rainfall change is accurate, yet diverge from some research studies. We analyze meteorological station rainfall data using metrics that are familiar to smallholders. Farmers' perceptions of rainfall in southern Ethiopia were explored through interviews conducted in three communities. Our findings identified some forms of convergence, as well as divergence, in farmers' perception of rainfall trends and meteorological station data results. In asking the question 'Why do data based on farmer experiences of rainfall variability differ from meteorological station data?', we show that using existing data and applying farmer-influenced metrics can improve the information shared with farmers. We argue that, under further climate change, it will be increasingly important to convey meteorological information to farmers in ways that are relevant to them and their agricultural livelihoods. • Smallholder farmer experiences and climate science often diverge. • We develop new metrics motivated by research with smallholders. • New metrics and analyses can bridge some divergences. • Methods developed are relevant for communicating climate science with farmers. [ABSTRACT FROM AUTHOR]