Search

The recharge of groundwater resources, which is an important source for drinking water supply in southwestern Germany, is affected by droughts. In order to manage groundwater resources sustainably, knowledge about groundwater recharge, especially under drought conditions, is indispensable. We investigate and compare groundwater recharge and groundwater levels during droughts in southwestern Germany with regard to their quantification, propagation and persistence. In particular, we investigate how groundwater recharge patterns change during droughts and how this affects groundwater levels. In addition, we investigate regional similarities of groundwater recharge patterns. Therefore, we compare measured groundwater levels with the model results of groundwater recharge of the spatial version of the hydrological model TRAIN. Groundwater droughts are detected with the help of a groundwater drought indicator and evaluated with regard to their spatial distribution. The incipient (modelled) groundwater recharge is displayed with heat map diagrams, which show the temporal anomalies of the incipient time. The dependency between groundwater recharge and groundwater drought is carried out by cross correlation analysis. We were able to show that the onset of the autumnal groundwater recharge in drought years is distinctly delayed. Another interesting finding is the spatial organization, where the model results show the strongest characteristic for the Upper Rhine Valley. According to our investigations, not only the time of onset of groundwater recharge in autumn, but also the extent of groundwater recharge in the following winter influences the propagation and persistence of a groundwater drought. Our findings will enable better decision-making processes for a sustainable water and aquifer management within the context of climate change. [ABSTRACT FROM AUTHOR]

There has been an accelerated and over-proportional rate of warming in the dry mid-latitudes and boreal forests of Southern Siberia. Associated changes affect permafrost distribution, the occurrence of wild fires and hydrological dynamics. Given that the Boreal ecotone occupies roughly 20 million km² of the global land surface, it can be assumed that these changes are of major interest with regard to the Earth's freshwater resources. However, since long-term hydro-meteorological time series are often not available, the impact of climate and environmental change on flow dynamics and water availability can only be roughly estimated. To gain insight into these challenging questions, we try to quantify the discharges and their temporal developments from two large-scale river basins. In a first step, we determine associated variabilities and trends of the major influencing factors, such as air temperature, precipitation and evapotranspiration. The selected catchments represent the variety of the climatic, landscape and permafrost patterns of that region: (1) Selenga River is the largest sub-basin of Lake Baikal, with a catchment size of about 440,000 km². The basin covers the transition belt between the dry mid-latitudes and the Boreal Zone and is mostly underlain by discontinuous permafrost. (2) Aldan River is a tributary of the Lena River. It drains an area of approx. 750,000 km², which is completely attributable to the Boreal ecotone and the continuous permafrost zone. Our analysis is based on long-term historical (1946-2015) hydro-meteorological time series, large-scale gridded data sets, as well as modeling simulations. The data undergoes extensive testing to detect anomalies, trends and multiple dependencies. The strong increase in air temperature during last 60 years may result in permafrost degradation and a decrease in seasonal frost occurrence, which is evident from the decreasing intra-annual variability of discharge in both catchments. However, the changes in river discharge show different directions: while the mean discharge of Selenga has decreased significantly, the mean discharge of Aldan shows a significant increase over the long-term period (based on the Mann Kendall test at a 95% confidence level). There also exist substantial seasonal shifts in the flow dynamics over both areas. These drastic and highly significant changes can be partly (but not fully) explained by precipitation and air temperature variabilities and trends. It is therefore likely that changes in landscape patterns, such as permafrost degradation and large-scale forest fires, are of great significance for the hydrological changes. Moreover, increasing water withdrawals due to a growing population, accelerated urbanization and a highly dynamic mining sector in the Selenga basin are factors that contribute to decreasing streamflow trends. To further clarify these relationships, our investigations will be extended to neighboring catchments, and our simulation studies will include an ensemble of hydrological models. [ABSTRACT FROM AUTHOR]