Search

Climate change, together with changes in land cover and water allocations, is expected to affect the availability of water resources. The long-term effect of these changes on available water resources in central Chile was comprehensively evaluated through climatic trends from 1982, land cover changes from 2001, and water allocations from 1980. Trends in climatic, land cover and hydrological variables were based on a wide range of data sources in combination with inter-annual climate variability analysis. Climate variables suggest trends that lead to a drier future. Land cover changes show increased agricultural and forestry extents, which have also shifted towards more southern regions, and a reduction in water and ice/snow covered areas. These changes have been encouraged by steady increases in water allocations. About 90% of evaluated gauging stations and 87% of analysed monitoring wells indicate declining trends. Future drier scenarios require further actions to address increasing water scarcity in Chile. [ABSTRACT FROM AUTHOR]

Rapid permafrost thaw and precipitation regime shifts are altering surface and subsurface hydrological processes in arctic and subarctic watersheds. Long-term data (40 years) from two large permafrost watersheds in northeastern China, the Tahe River and Duobukuer River watersheds, indicate that winter baseflows are characterized by significant positive trends of 1.7% and 2.5%·year-1, respectively. Winter baseflows exhibited statistically significant positive correlations with mean annual air temperature and the thawing index, an indicator of permafrost degradation, for both watersheds, as well as the increasing annual rainfall fraction of precipitation for the Duobukuer River watershed. Winter baseflows were characterized by a breakpoint in 1989, which lagged behind the mean annual air temperature breakpoint by only two years. The statistical analyses suggest that the increases in winter baseflow are likely related to enhanced groundwater storage and winter groundwater discharge caused by permafrost thaw and are potentially also due to an increase in the wet season rainfall. These hydrological trends are first apparent in marginal areas of permafrost distribution and are expected to shift northward towards formerly continuous permafrost regions in the context of future climate warming. [ABSTRACT FROM AUTHOR]

Highlights: [•] Summer river flows in central Karakoram conspicuously exhibit rising trends. [•] Rate of loss of glacial storage is approximately 0.04–0.05mm/day/year. [•] Increasing summer precipitation is responsible for nonnegative glacial mass balance. [•] Rising river flows accompany nonnegative glacial mass balance in central Karakoram. [ABSTRACT FROM AUTHOR]

Many climate change studies have shown that streamflow has been changing across the US over the last century. However, there are fewer studies examining trends in hydrologic variables such as soil moisture and snow, which tend to be poorly observed in some regions. Hydrologic models can be applied to understand changes in processes with limited spatial or temporal observational records. However, the application of hydrologic models to long time periods can be complicated by human influences on the hydrologic cycle. In this study, we explore hydrologic changes and the applicability of a commonly used hydrologic modelling system for climate change analysis in a heavily managed landscape. Historical streamflow observations and model-derived time series of subsurface storage, frozen ground, and snow cover were analysed for 10 Iowa watersheds. The modelled data were generated using precipitation and temperature data spanning 1948-2003 as inputs to common hydrologic prediction models. Time series were tested for trends and significance using the Mann-Kendall (MK) test with the Trend-Free Pre-Whitening procedure at a p = 0.1 significance level. Plots of 10-year running averages were also examined. Significantly increasing trends in mean daily discharge and the number of high-flow days were found for several watersheds. Increasing monthly subsurface water content was observed throughout the year in most basins, and was greatest during the winter. The number of modelled frozen-ground days declined at all sites. Three different model calibration periods were tested and found to reproduce the general upward trend observed in the daily mean discharge. However, the model results varied from the observed in both magnitude and the number of sites identified to have MK trends. Additional functionality that considers land management and land cover change may make the models applied here more accurate for studying climate change impacts in regions such as Iowa. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]