This study investigated spatial and temporal variations of extreme precipitation over Yunnan Province during 1960-2012. On the basis of a dataset from 120 meteorological stations covering the region, ten precipitation indices derived from daily precipitation were computed and analysed. Our results indicate the precipitation indices showed spatially complex trends. Most precipitation indices present increasing trends in western Yunnan and decreasing trends in eastern Yunnan. The western, southern and central regions experienced an increase in consecutive dry days (CDDs) and decrease in consecutive wet days (CWDs). In addition, a widespread increase was also found in precipitation intensity over Yunnan. On a region-wide scale, a weak decrease was observed in total precipitation, accompanied by an increase in precipitation intensity. CDDs tended to be prolonged while the CWDs tended to be shortened. The days with precipitation amounts totaling more than 10 mm and maximum 5-day precipitation amount had decreasing but not significant trends. In contrast, insignificant increases were found for the maximum 1-day precipitation and annual total precipitation exceeding 95th and 99th percentiles. The contribution of extreme precipitation to total precipitation increased during 1960-2012. Overall, occurrences of extreme precipitation are more concentrated in time. The weakening of the Asian summer monsoon strength and local topography had contribution to the variations of extreme precipitation over Yunnan. However, the forcing mechanisms are very complicated and need to be studied in subsequent work.

Satellite-based products with high spatial and temporal resolution provide useful precipitation information for data-sparse or ungauged large-scale watersheds. In the Lower Lancang-Mekong River Basin, rainfall stations are sparse and unevenly distributed, and the transboundary characteristic makes the collection of precipitation data more difficult, which has restricted hydrological processes simulation. In this study, daily precipitation data from four datasets (gauge observations, inverse distance weighted (IDW) data, Tropical Rainfall Measuring Mission (TRMM) estimates, and Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) estimates), were applied to drive the Soil and Water Assessment Tool (SWAT) model, and then their capability for hydrological simulation in the Lower Lancang-Mekong River Basin were examined. TRMM and CHIRPS data showed good performances on precipitation estimation in the Lower Lancang-Mekong River Basin, with the better performance for TRMM product. The Nash-Sutcliffe efficiency (NSE) values of gauge, IDW, TRMM, and CHIRPS simulations during the calibration period were 0.87, 0.86, 0.95, and 0.93 for monthly flow, respectively, and those for daily flow were 0.75, 0.77, 0.86, and 0.84, respectively. TRMM and CHIRPS data were superior to rain gauge and IDW data for driving the hydrological model, and TRMM data produced the best simulation performance. Satellite-based precipitation estimates could be suitable data sources when simulating hydrological processes for large data-poor or ungauged watersheds, especially in international river basins for which precipitation observations are difficult to collect. CHIRPS data provide long precipitation time series from 1981 to near present and thus could be used as an alternative precipitation input for hydrological simulation, especially for the period without TRMM data. For satellite-based precipitation products, the differences in the occurrence frequencies and amounts of precipitation with different intensities would affect simulation results of water balance components, which should be comprehensively considered in water resources estimation and planning.

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Abstract:Accurate precipitation data at a high spatial resolution are essential for hydrological, meteorological, and ecological research at regional scales. This study presented a geostatistical downscaling-calibration procedure to derive the high spatial resolution maps of precipitation over a mountainous watershed affected by a monsoon climate. Based on the relationships between precipitation and other environmental variables, such as the Normalized Difference Vegetation Index (NDVI) and digital elevation model (DEM), a regression model with a residual correction method was applied to downscale the Tropical Rainfall Measuring Mission (TRMM) 3B43 product from coarse resolution (25 km) to fine resolution (1 km). Two methods, geographical difference analysis (GDA) and geographical ratio analysis (GRA), were used to calibrate the downscaled TRMM precipitation data. Monthly 1 km precipitation data were obtained by disaggregating 1 km annual downscaled and calibrated precipitation data using monthly fractions derived from original TRMM data. The downscaled precipitation datasets were validated against ground observations measured by rain gauges. According to the comparison of different regression models and residual interpolation methods, a geographically-weighted regression kriging (GWRK) method was accepted to conduct the downscaling of TRMM data. The downscaled TRMM precipitation data obtained using GWRK described the spatial patterns of precipitation reasonably well at a spatial resolution of 1 km with more detailed information when compared with the original TRMM precipitation. The results of validation indicated that the GRA method provided results with higher accuracy than that of the GDA method. The final annual and monthly downscaled precipitation not only had significant improvement in spatial resolution, but also agreed well with data from the validation rain gauge stations (i.e., R 2 = 0.72, RMSE = 161.0 mm, MAE = 127.5 mm, and Bias = 0.050 for annual downscaled precipitation during 2001 to 2015; and R 2 = 0.91, RMSE = 22.2 mm, MAE = 13.5 mm, and Bias = 0.048 for monthly downscaled precipitation during 2001 to 2015). In general, the downscaling-calibration procedure is useful for complex mountainous areas with insufficient ground gauges.

China is Asia's most important upstream riparian country, sharing 110 rivers and lakes with 18 downstream countries. Consequently, China's management of transboundary water resources must consider both environmental and geopolitical risks.The major threats to and conflicts over international rivers in China revolve around biotic homogenisation due to the installation of transport links, water allocation, water pollution, alteration of natural flow patterns and disruption of fisheries due to the installation of hydropower dams, and droughts and floods exacerbated by climate change. Because these problems have an international component, they fall under China's Peaceful Rise strategy, mandating that transboundary conflicts be resolved amicably as part of the overarching goal of increasing regional economic growth with as little conflict as possible.Science-backed policy is more likely to result in long term, mutually agreeable solutions; the results of applied ecological research have already resulted in a number of mitigation measures, including setting operational thresholds to reduce the downstream impact of dams, designating protected areas along key river stretches where dams cannot be installed (one dam in a critical location has been cancelled), and the installation of terrestrial protected-area networks.Synthesis and applications. Applied ecology will continue to play an important role in the diagnosis and resolution of environmental threats to China's transboundary waters. More importantly, applied ecology can inform the development of a transboundary environmental compensation mechanism and regional consultative mechanisms that support informed, cooperative decision-making for China and its riparian neighbours.

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