Abstract
Distributed hydrological simulation in karst regions has always been a challenging task because of their unique hydrogeological characteristics. The karst mountain region of southwest China (KMRSC), one of the largest continuous karst areas in the world, contributes to about 54 percent of water supply in the basins. In spite of its importance, we have a poor understanding of the evolution laws of hydrological cycle and water resources in KMRSC. We developed a physically-based, distributed hydrological model, called Water and Energy transfer Processes (WEP)-karst model, for KMRSC by introducing the equivalent porous medium approach to the WEP-L model, and dividing the modelling domain into 2021 sub-watersheds. The area of sub-watersheds ranges from 55 to 920 km2, with an average value of 170 km2. The model showed a good performance in simulating the monthly discharge at 18 representative hydrological stations, with the Nash–Sutcliffe efficiency (NSE) values ranging from 0.71 to 0.94, and the relative error (RE) values from −9.8% to 8.3% during the validation period (1980–2000). Then, we employed an in-depth analysis of the temporal and spatial variation of main water cycle fluxes, including precipitation, infiltration, evapotranspiration, blue water (i.e., river runoff), and green water (i.e., vegetation transpiration) over 1956–2015. In addition, the impact of climate change on these fluxes was evaluated under the median emission scenario (RCP4.5). The results showed that: (1) annual average precipitation of KMRSC reached 1506 mm, which is 2.4 times of the national average level, and about 47% (701 mm) of it contributed to river runoff. The infiltration and evapotranspiration were 862 and 870 mm, respectively. The transpiration from plants and trees accounted for 51% of the evapotranspiration. (2) Except for the green water, other fluxes experienced a significant decrease over the past 60 years. Blue water showed the largest interannual fluctuation and the strongest sensitivity to climate change. (3) Both precipitation and infiltration concentrated from May to August, and blue water increased notably from May to June and peaked in June. Blue water and precipitation were more likely to decrease in the future over 2021–2050 due to the climate change.
Highlights
Water is critical for industrial and agricultural production and ecological sustainability
The lumped models are often used for large-scale basins, where a karst aquifer is considered as a unit that converts input functions into output signals [11,12,13]
By introducing equivalent porous medium approach into the Water and Energy transfer Processes (WEP)-L distributed hydrological model, the WEP-karst model was developed for an enhanced description of the karst landforms characteristics
Summary
Water is critical for industrial and agricultural production and ecological sustainability. The lumped (or conceptual) models are often used for large-scale basins, where a karst aquifer is considered as a unit that converts input functions (e.g., precipitation) into output signals (e.g., spring discharge) [11,12,13] As a result, these models are very limited in describing the spatial variability of hydrological processes in the karst catchments. By selecting the whole KMRSC as the study area, rather than an experimental small basin, this paper attempted to examine the spatiotemporal variation of regional water cycle fluxes For this purpose, by introducing equivalent porous medium approach into the WEP-L distributed hydrological model, the WEP-karst model was developed for an enhanced description of the karst landforms characteristics. Green water was defined as vegetation evaporation (i.e., rainwater used efficiently by the vegetation), which is an important indicator of the ecology of mountain vegetation
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