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Crop producers face significant and increasing drought risks. We evaluate whether insurances based on globally and freely available satellite-retrieved soil moisture data can reduce farms’ financial drought risk exposure. We design farm individual soil moisture index insurances for wheat, maize and rapeseed production using a case study for Eastern Germany. We find that the satellite-retrieved soil moisture index insurances significantly decrease risk exposure for these crops compared to the situation where production is not insured. The satellite-retrieved index also outperforms one based on soil moisture estimates derived from meteorological measurements at ground stations. Important implications for insurers and policy makers are that they could and should develop better suited insurances. Available satellite-retrieved data can be used to increase farmers’ resilience in a changing climate., European Review of Agricultural Economics, ISSN:0165-1587, ISSN:1464-3618

Actual land evapotranspiration (ET) is a key component of the global hydrological cycle and an essential variable determining the evolution of hydrological extreme events under different climate change scenarios. However, recently available ET products show persistent uncertainties that are impeding a precise attribution of human-induced climate change. Here, we aim at comparing a range of independent global monthly land ET estimates with historical model simulations from the global water, agriculture, and biomes sectors participating in the second phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). Among the independent estimates, we use the EartH2Observe Tier-1 dataset (E2O), two commonly used reanalyses, a pre-compiled ensemble product (LandFlux-EVAL), and an updated collection of recently published datasets that algorithmically derive ET from observations or observations-based estimates (diagnostic datasets). A cluster analysis is applied in order to identify spatio-temporal differences among all datasets and to thus identify factors that dominate overall uncertainties. The clustering is controlled by several factors including the model choice, the meteorological forcing used to drive the assessed models, the data category (models participating in the different sectors of ISIMIP2a, E2O models, diagnostic estimates, reanalysis-based estimates or composite products), the ET scheme, and the number of soil layers in the models. By using these factors to explain spatial and spatio-temporal variabilities in ET, we find that the model choice mostly dominates (24%–40% of variance explained), except for spatio-temporal patterns of total ET, where the forcing explains the largest fraction of the variance (29%). The most dominant clusters of datasets are further compared with individual diagnostic and reanalysis-based estimates to assess their representation of selected heat waves and droughts in the Great Plains, Central Europe and western Russia. Although most of the ET estimates capture these extreme events, the generally large spread among the entire ensemble indicates substantial uncertainties.

Land evapotranspiration (ET) estimates are available from several global data sets. Here, monthly global land ET synthesis products, merged from these individual data sets over the time periods 1989–1995 (7 yr) and 1989–2005 (17 yr), are presented. The merged synthesis products over the shorter period are based on a total of 40 distinct data sets while those over the longer period are based on a total of 14 data sets. In the individual data sets, ET is derived from satellite and/or in situ observations (diagnostic data sets) or calculated via land-surface models (LSMs) driven with observations-based forcing or output from atmospheric reanalyses. Statistics for four merged synthesis products are provided, one including all data sets and three including only data sets from one category each (diagnostic, LSMs, and reanalyses). The multi-annual variations of ET in the merged synthesis products display realistic responses. They are also consistent with previous findings of a global increase in ET between 1989 and 1997 (0.13 mm yr−2 in our merged product) followed by a significant decrease in this trend (−0.18 mm yr−2), although these trends are relatively small compared to the uncertainty of absolute ET values. The global mean ET from the merged synthesis products (based on all data sets) is 493 mm yr−1 (1.35 mm d−1) for both the 1989–1995 and 1989–2005 products, which is relatively low compared to previously published estimates. We estimate global runoff (precipitation minus ET) to 263 mm yr−1 (34 406 km3 yr−1) for a total land area of 130 922 000 km2. Precipitation, being an important driving factor and input to most simulated ET data sets, presents uncertainties between single data sets as large as those in the ET estimates. In order to reduce uncertainties in current ET products, improving the accuracy of the input variables, especially precipitation, as well as the parameterizations of ET, are crucial., Hydrology and Earth System Sciences, 17 (10), ISSN:1027-5606, ISSN:1607-7938

This article extends a previous study Seneviratne et al. (2016) to provide regional analyses of changes in climate extremes as a function of projected changes in global mean temperature. We introduce the DROUGHT-HEAT Regional Climate Atlas, an interactive tool to analyse and display a range of well-established climate extremes and water-cycle indices and their changes as a function of global warming. These projections are based on simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). A selection of example results are presented here, but users can visualize specific indices of interest using the online tool. This implementation enables a direct assessment of regional climate changes associated with global mean temperature targets, such as the 2 and 1.5° limits agreed within the 2015 Paris Agreement., Geoscientific Model Development, 10 (9), ISSN:1991-9603, ISSN:1991-959X

The evolution of near‐surface air temperature is influenced by various dynamical, radiative, and surface‐atmosphere exchange processes whose contributions are still not completely quantified. Applying stepwise multiple linear regression to Coupled Model Intercomparison Project phase 5 (CMIP5) model simulations and focusing on radiation (diagnosed by incoming shortwave and incoming longwave radiation) and land surface conditions (diagnosed by soil moisture and albedo) about 79% of the interannual variability and 99% of the multidecadal trend of monthly mean daily maximum temperature over land can be explained. The linear model captures well the temperature variability in middle‐to‐high latitudes and in regions close to the equator, whereas its explanatory potential is limited in deserts. While radiation is an essential explanatory variable over almost all of the analyzed domain, land surface conditions show a pronounced relation to temperature in some confined regions. These findings highlight that considering local‐to‐regional processes is crucial for correctly assessing interannual temperature variability and future temperature trends., Geophysical Research Letters, 45 (10), ISSN:0094-8276, ISSN:1944-8007

Actual land evapotranspiration (ET) is a key component of the global hydrological cycle and an essential variable determining the evolution of hydrological extreme events under different climate change scenarios. However, recently available ET products show persistent uncertainties that are impeding a precise attribution of human-induced climate change. Here, we aim at comparing a range of independent global monthly land ET estimates with historical model simulations from the global water, agriculture, and biomes sectors participating in the second phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). Among the independent estimates, we use the EartH2Observe Tier-1 dataset (E2O), two commonly used reanalyses, a pre-compiled ensemble product (LandFlux-EVAL), and an updated collection of recently published datasets that algorithmically derive ET from observations or observations-based estimates (diagnostic datasets). A cluster analysis is applied in order to identify spatio-temporal differences among all datasets and to thus identify factors that dominate overall uncertainties. The clustering is controlled by several factors including the model choice, the meteorological forcing used to drive the assessed models, the data category (models participating in the different sectors of ISIMIP2a, E2O models, diagnostic estimates, reanalysis-based estimates or composite products), the ET scheme, and the number of soil layers in the models. By using these factors to explain spatial and spatio-temporal variabilities in ET, we find that the model choice mostly dominates (24%–40% of variance explained), except for spatio-temporal patterns of total ET, where the forcing explains the largest fraction of the variance (29%). The most dominant clusters of datasets are further compared with individual diagnostic and reanalysis-based estimates to assess their representation of selected heat waves and droughts in the Great Plains, Central Europe and western Russia. Although most of the ET estimates capture these extreme events, the generally large spread among the entire ensemble indicates substantial uncertainties., Environmental Research Letters, 13 (7), ISSN:1748-9326, ISSN:1748-9318

This paper presents an update of a basin-scale diagnostic dataset of monthly variations in terrestrial water storage for large river basins worldwide (BSWB v2016, doi:10.5905/ethz-1007-82). Terrestrial water storage comprises all forms of water storage on land surfaces, and its seasonal and inter-annual variations are mostly determined by soil moisture, groundwater, snow cover, and surface water. The dataset presented is derived using a combined atmospheric and terrestrial water-balance approach with conventional streamflow measurements and reanalysis data of atmospheric moisture flux convergence. It extends a previous, existing version of the dataset (Mueller et al., 2011) temporally and spatially., Earth System Science Data, 9 (1), ISSN:1866-3516, ISSN:1866-3508

The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project aims to advance the development of land evaporation estimates on global and regional scales. Its main objective is the derivation, validation, and intercomparison of a group of existing evaporation retrieval algorithms driven by a common forcing data set. Three commonly used process-based evaporation methodologies are evaluated: the Penman–Monteith algorithm behind the official Moderate Resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Global Land Evaporation Amsterdam Model (GLEAM), and the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL). The resulting global spatiotemporal variability of evaporation, the closure of regional water budgets, and the discrete estimation of land evaporation components or sources (i.e. transpiration, interception loss, and direct soil evaporation) are investigated using river discharge data, independent global evaporation data sets and results from previous studies. In a companion article (Part 1), Michel et al. (2016) inspect the performance of these three models at local scales using measurements from eddy-covariance towers and include in the assessment the Surface Energy Balance System (SEBS) model. In agreement with Part 1, our results indicate that the Priestley and Taylor products (PT-JPL and GLEAM) perform best overall for most ecosystems and climate regimes. While all three evaporation products adequately represent the expected average geographical patterns and seasonality, there is a tendency in PM-MOD to underestimate the flux in the tropics and subtropics. Overall, results from GLEAM and PT-JPL appear more realistic when compared to surface water balances from 837 globally distributed catchments and to separate evaporation estimates from ERA-Interim and the model tree ensemble (MTE). Nonetheless, all products show large dissimilarities during conditions of water stress and drought and deficiencies in the way evaporation is partitioned into its different components. This observed inter-product variability, even when common forcing is used, suggests that caution is necessary in applying a single data set for large-scale studies in isolation. A general finding that different models perform better under different conditions highlights the potential for considering biome- or climate-specific composites of models. Nevertheless, the generation of a multi-product ensemble, with weighting based on validation analyses and uncertainty assessments, is proposed as the best way forward in our long-term goal to develop a robust observational benchmark data set of continental evaporation., Hydrology and Earth System Sciences, 20 (2), ISSN:1027-5606, ISSN:1607-7938

This paper presents a community effort to develop good practice guidelines for the validation of global coarse-scale satellite soil moisture products. We provide theoretical background, a review of state-of-the-art methodologies for estimating errors in soil moisture data sets, practical recommendations on data pre-processing and presentation of statistical results, and a recommended validation protocol that is supplemented with an example validation exercise focused on microwave-based surface soil moisture products. We conclude by identifying research gaps that should be addressed in the near future., Remote Sensing of Environment, 244, ISSN:0034-4257

Environmental Research Letters, 14 (11), ISSN:1748-9326, ISSN:1748-9318

The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project has compiled a forcing data set covering the period 2005–2007 that aims to maximize the exploitation of European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run four established ET algorithms: the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman–Monteith algorithm from the MODerate resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Surface Energy Balance System (SEBS) and the Global Land Evaporation Amsterdam Model (GLEAM). In addition, in situ meteorological data from 24 FLUXNET towers were used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed on several timescales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement with the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements (R2 = 0.67), the agreement of the satellite-based ET estimates is only marginally lower (R2 = 0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85 towers (model inputs resampled to a common grid to facilitate global estimates) confirmed the original findings., Hydrology and Earth System Sciences, 20 (2), ISSN:1027-5606, ISSN:1607-7938

Terrestrial climate is influenced by various land–atmosphere interactions that involve numerous land surface state variables. In several regions on Earth, soil moisture plays an important role for climate via its control on the partitioning of net radiation into sensible and latent heat fluxes; consequently, soil moisture also impacts on temperature and precipitation. The Global Land–Atmosphere Coupling Experiment–Coupled Model Intercomparison Project phase 5 (GLACE-CMIP5) aims to quantify the impact of soil moisture on these important climate variables and to trace the individual coupling mechanisms. GLACE-CMIP5 provides experiments with different soil moisture prescriptions that can be used to isolate the effect of soil moisture on climate. Using a theoretical framework that relies on the distinct relation of soil moisture with evaporative fraction (the ratio of latent heat flux over net radiation) in different soil moisture regimes, the climate impact of the soil moisture prescriptions in the GLACE-CMIP5 experiments can be emulated and quantified. The framework-based estimation of the soil moisture effect on the evaporative fraction agrees very well with estimations obtained directly from the GLACE-CMIP5 experiments (pattern correlation of 0.85). Moreover, the soil moisture effect on the daily maximum temperature is well captured in regions where soil moisture exerts a strong control on latent heat fluxes. The theoretical approach is further applied to quantify the soil moisture contribution to the projected change of the temperature on the hottest day of the year, confirming recent estimations by other studies. Finally, GLACE-style soil moisture prescriptions are emulated in an extended set of CMIP5 models. The results indicate consistency between the soil moisture–climate coupling strength estimated with the GLACE-CMIP5 and the CMIP5 models. Although the theoretical approach is only designed to capture the local soil moisture–climate coupling strength, it can also help to distinguish non-local from local soil moisture–atmosphere feedbacks where sensitivity experiments (such as GLACE-CMIP5) are available. Overall, the theoretical framework-based approach presented here constitutes a simple and powerful tool to quantify local soil moisture–climate coupling in both the GLACE-CMIP5 and CMIP5 models that can be applied in the absence of dedicated sensitivity experiments., Earth System Dynamics, 9 (4), ISSN:2190-4987, ISSN:2190-4979

Energy and water fluxes between the land and the atmosphere strongly depend on the state of the land surface. A key process in this respect is the control of soil moisture on the partitioning of net radiation into latent and sensible heat fluxes. Especially near-surface air temperatures can be considerably affected by modified shares of these fluxes. Different metrics have been developed to assess the soil moisture effects on latent heat flux, on near-surface air temperature, and on other climate variables. In this thesis, the soil moisture--climate coupling strength is quantified by employing a simple framework that connects evaporative fraction $\mathrm{EF}$ (the amount of net radiation used for latent heat flux) to soil moisture $\theta$. This $\mathrm{EF}(\theta)$ framework allows to differentiate between dry, transitional, and wet soil moisture regimes, each having a distinct soil moisture control on the surface heat fluxes. Additionally, the contributions of different land surface variables and radiation components to near-surface air temperature variability are estimated. In the first part of this thesis, the $\mathrm{EF}(\theta)$ framework is used to estimate the spatial and temporal occurrence of the soil moisture regimes for three different data sources (two reanalysis datasets and a combination of observation-based datasets with a remote-sensing driven land surface model). The transitional regime, in which soil moisture affects evaporative fraction and thus possibly also near-surface air temperature, can be found in multiple regions of the world, such as Africa, India, and Australia. The regime classification allows furthermore to quantify the soil moisture--temperature coupling strength separately in the different soil moisture regimes. In several regions of the world, soil moisture variations in the transitional regime substantially impact near-surface air temperature. In contrast, soil moisture effects on temperature are almost negligible in the wet regime. Passages between the soil moisture regimes due to seasonal weather and climate variations can lead to changing soil moisture--temperature coupling strengths in the course of the year. The distinct soil moisture effects on evaporative fraction and near-surface air temperature in the different soil moisture regimes highlight the suitability of the $\mathrm{EF}(\theta)$ framework to assess spatial and temporal variations of soil moisture--climate coupling. In the second part of the thesis, the $\mathrm{EF}(\theta)$ framework is further used to quantify the impact of soil moisture on climate in a set of idealized climate model experiments. The Global Land-Atmosphere Climate Experiment--Coupled Model Intercomparison Project phase 5 (GLACE-CMIP5) includes three idealized simulations with diverse soil moisture prescriptions that allow to study the influence of different soil moisture levels on atmospheric conditions. The impact of soil moisture differences between the GLACE-CMIP5 experiments can be explained by a theoretical estimation of the soil moisture effect on evaporative fraction that is based on the sensitivities in the different soil moisture regimes of the $\mathrm{EF}(\theta)$ framework. The resulting soil moisture effects on evaporative fraction agree well with estimations obtained directly from the GLACE-CMIP5 experiments. Similarly, the theoretical estimation captures the soil moisture effects on temperature well in regions where soil moisture exerts a strong control on latent heat fluxes. The theoretical approach can further be used to quantify the soil moisture contribution to projected future increases of the temperature on the hottest day of the year, confirming the results of recent estimations by other studies. As for the theoretical estimation only data of the interactive simulation are needed, it can additionally be used to emulate GLACE-CMIP5-style soil moisture prescription experiments with an extended set of models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). The CMIP5 models generally agree with the GLACE-CMIP5 models on the regions where soil moisture shifts significantly impact near-surface air temperatures and, additionally, yield more robust and reliable estimations of the geographical patterns with strong soil moisture--climate coupling. Although the theoretical approach is designed to capture only the local soil moisture effects on climate, it also enables to differentiate local from non-local soil moisture--atmosphere feedbacks where sensitivity experiments (such as GLACE-CMIP5) are available. The theoretical approach constitutes thus a simple and powerful tool to quantify soil moisture--climate coupling in both GLACE-CMIP5 and CMIP5 models without the need of performing additional simulations. In the third part of the thesis, the contribution of several land surface variables and radiation components to near-surface air temperature variability is estimated using CMIP5 model output. Employing stepwise multiple linear regression and focusing on incoming shortwave radiation, incoming longwave radiation, land surface albedo, and soil moisture as explanatory variables a large fraction of interannual temperature variability and almost all of the multidecadal temperature trend on land can be explained. While the radiation components are essential explanatory variables for almost all land area, albedo and soil moisture significantly contribute to the model performance in some confined regions. This highlights the dominating role of radiation and atmospheric processes for near-surface air temperature variability that can, however, also substantially be impacted by the state of the land surface. Overall, the results of this thesis emphasize the suitability of the soil moisture regime classification to describe the soil moisture effect on atmospheric conditions in several reanalyses, global climate models, and a remote-sensing driven land surface model. Soil moisture impacts on near-surface air temperature are additionally found to act at different timescales, highlighting the importance of a proper understanding of soil moisture--climate coupling both for short-term temperature variability as well as for long-term temperature trends.