Why has catchment evaporation increased in the past 40 years? A data-based study in Austria

Regional evaporation has increased in many parts of the world in the last decades, but the drivers of these increases are widely debated. Part of the difficulty lies in the scarcity of high-quality long-term data on evaporation. In this paper, we analyze changes in catchment evaporation estimated from the water balances of 156 catchments in Austria over the period 1977–2014 and attribute them to changes in atmospheric demand and available energy, vegetation, and precipitation as possible drivers. Trend analyses suggest that evaporation has significantly increased in 60&thinsp;% of the catchments (p ≤ 0.05) with an average increase of 29±14&thinsp;mm&thinsp;yr−1&thinsp;decade−1 (±&thinsp;standard deviation) or 4.9±2.3&thinsp;%&thinsp;decade−1. Pan evaporation based on 24 stations has, on average, increased by 29±5&thinsp;mm&thinsp;yr−1&thinsp;decade−1 or 6.0±1.0&thinsp;%&thinsp;decade−1. Reference evaporation over the 156 catchments estimated by the Penman–Monteith equation has increased by 18±5&thinsp;mm&thinsp;yr−1&thinsp;decade−1 or 2.8±0.7&thinsp;%&thinsp;decade−1. Of these, 2.1&thinsp;% are due to increased global radiation and 0.5&thinsp;% due to increased air temperature according to the Penman–Monteith equation. A satellite-based vegetation index (NDVI) has increased by 0.02±0.01&thinsp;decade−1 or 3.1±1.1&thinsp;%&thinsp;decade−1. Estimates of reference evaporation accounting for changes in stomata resistance due to changes in the NDVI indicate that the increase in vegetation activity has led to a similar increase in reference evaporation as changes in the climate parameters. A regression between trends in evaporation and precipitation yields a sensitivity of a 0.22±0.05&thinsp;mm&thinsp;yr−2 increase in evaporation to a 1&thinsp;mm&thinsp;yr−2 increase in precipitation. A synthesis of the data analyses suggests that 43±15&thinsp;% of the observed increase in catchment evaporation may be directly attributed to increased atmospheric demand and available energy, 34±14&thinsp;% to increased vegetation activity, and 24±5&thinsp;% to increases in precipitation.</p

Analysis of changes in climate and river discharge with focus on seasonal runoff predictability in the Aksu River Basin

The River Aksu is the principal tributary to the River Tarim, providing about three quarters of its discharge. It originates in Kyrgyzstan and flows into the arid areas of the Xinjiang Uyghur Autonomous Region in China, where an extensive irrigated agriculture has been developed in the river oases. The aim of the present contribution is to review the current trends in temperature, precipitation, and river discharge and links between these variables. The temperature in the region and the river discharge have been rising. Changes were studied using multiple trend analyses with different start and end years. Correlations between daily temperature and discharge are high and statistically significant for two headwater subcatchments of the Aksu for most of the time. However, there are episodes in late summer or beginning of autumn when correlations between temperature and discharge for the Xiehela station are absent. This can only be explained by Glacial Lake Outburst Floods from the Lake Merzbacher that are not routinely monitored. On an annual time scale, changes in summer discharge in the highly glacierized Xiehela subcatchment are dominated by changes in temperature. In contrast, in the subcatchment Shaliguilanke, variations in summer streamflow are more strongly influenced by variations in precipitation. A comparison of links between climatic variables and streamflow at different temporal scales is offered. Perspectives for seasonal forecasting are examined

An Inventory of Mitigation Methods and Guide to their Effects on Diffuse Water Pollution, Greenhouse Gas Emissions and Ammonia Emissions from Agriculture

Prepared as part of Defra Project WQ010

Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change in the 21st century

During the past several decades, the Earth system has changed significantly, especially across Northern Eurasia. Changes in the socio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that can have global consequences. The Northern Eurasia Future Initiative (NEFI) has been designed as an essential continuation of the Northern Eurasia Earth Science Partnership Initiative (NEESPI), which was launched in 2004. NEESPI sought to elucidate all aspects of ongoing environmental change, to inform societies and, thus, to better prepare societies for future developments. A key principle of NEFI is that these developments must now be secured through science-based strategies co-designed with regional decision makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and models have created a solid knowledge base to support the NEFI program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To address these questions, nine research foci are identified and their selections are briefly justified. These foci include: warming of the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreat of the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land-use; changes in infrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia's role in the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., mega-fires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current human activities (e.g., large scale water withdrawals, land use and governance change) and potentially restrict or provide new opportunities for future human activities. Therefore, we propose that Integrated Assessment Models are needed as the final stage of global change assessment. The overarching goal of this NEFI modeling effort will enable evaluation of economic decisions in response to changing environmental conditions and justification of mitigation and adaptation efforts

The Unexploited Treasures of Hydrological Observations Beyond Streamflow for Catchment Modeling

While measured streamflow is commonly used for hydrological model evaluation and calibration, an increasing amount of data on additional hydrological variables is available. These data have the potential to improve process consistency in hydrological modeling and consequently for predictions under change, as well as in data‐scarce or ungauged regions. Here, we show how these hydrological data beyond streamflow are currently used for model evaluation and calibration. We consider storage and flux variables, namely snow, soil moisture, groundwater level, terrestrial water storage, evapotranspiration, and altimetric water level. We aim at summarizing the state‐of‐the‐art and providing guidance for the use of additional hydrological variables for model evaluation and calibration. Based on a review of the current literature, we summarize observation methods and uncertainties of currently available data sets, challenges regarding their implementation, and benefits for model consistency. The focus is on catchment modeling studies with study areas ranging from a few km 2 to ~500,000 km 2 . We discuss challenges for implementing alternative variables that are related to differences in the spatio‐temporal resolution of observations and models, as well as to variable‐specific features, for example, discrepancy between observed and simulated variables. We further discuss advancements required to deal with uncertainties of the hydrological data and to integrate multiple, potentially inconsistent datasets. The increased model consistency and improvement shown by most reviewed studies regarding the additional variables often come at the cost of a slight decrease in streamflow model performance

The Unexploited Treasures of Hydrological Observations Beyond Streamflow for Catchment Modeling

While measured streamflow is commonly used for hydrological model evaluation and calibration, an increasing amount of data on additional hydrological variables is available. These data have the potential to improve process consistency in hydro- logical modeling and consequently for predictions under change, as well as in data-scarce or ungauged regions. Here, we show how these hydrological data beyond streamflow are currently used for model evaluation and calibration. We consider storage and flux variables, namely snow, soil moisture, groundwater level, terrestrial water storage, evapotranspiration, and altimetric water level. We aim at summarizing the state-of-the-art and providing guidance for the use of additional hydrological variables for model evaluation and calibration. Based on a review of the current literature, we summarize observation methods and un- certainties of currently available data sets, challenges regarding their implementation, and benefits for model consistency. The focus is on catchment modeling studies with study areas ranging from a few km 2 to ~500,000 km 2 . We discuss challenges for implementing alternative variables that are related to differences in the spatio-temporal resolution of observations and models, as well as to variable-specific features, for example, discrepancy between observed and simulated variables. We further discuss advancements required to deal with uncertainties of the hydrological data and to integrate multiple, potentially inconsistent datasets. The increased model consistency and improvement shown by most reviewed studies regarding the additional variables often come at the cost of a slight decrease in streamflow model performance

Hydrology : Asian glaciers are a reliable water source

PostprintPeer reviewe

Global-scale hydrological response to future glacier mass loss

Worldwide glacier retreat and associated future runoff changes raise major concerns over the sustainability of global water resources1,2,3,4, but global-scale assessments of glacier decline and the resulting hydrological consequences are scarce5,6. Here we compute global glacier runoff changes for 56 large-scale glacierized drainage basins to 2100 and analyse the glacial impact on streamflow. In roughly half of the investigated basins, the modelled annual glacier runoff continues to rise until a maximum (‘peak water’) is reached, beyond which runoff steadily declines. In the remaining basins, this tipping point has already been passed. Peak water occurs later in basins with larger glaciers and higher ice-cover fractions. Typically, future glacier runoff increases in early summer but decreases in late summer. Although most of the 56 basins have less than 2% ice coverage, by 2100 one-third of them might experience runoff decreases greater than 10% due to glacier mass loss in at least one month of the melt season, with the largest reductions in central Asia and the Andes. We conclude that, even in large-scale basins with minimal ice-cover fraction, the downstream hydrological effects of continued glacier wastage can be substantial, but the magnitudes vary greatly among basins and throughout the melt season