Quantifying the Impacts of Climate Change and Human Activities on Runoff in the Lancang River Basin Based on the Budyko Hypothesis

Based on the Lancang River Basin (LRB) hydro–meteorological data from 1961 to 2015, this study uses the Mann–Kendall trend test and mutation test to analyze the trend of hydro–meteorological variables, as well as which year the runoff series changes, respectively. We applied the Choudhury–Yang equation to calculate the climate and catchment landscape elasticity of runoff. Then we quantified the impact of climate change and human activities on runoff change. The results show that: (1) the mean annual precipitation (P) in LRB showed an insignificant decline, the annual potential evapotranspiration (E0) showed a significant increase, and the runoff depth (R) showed a significant decrease; (2) the abrupt change of the R occurred in 2005. Both the climate and catchment landscape elasticity of runoff increased, which means that the hydrological process of LRB became more sensitive to climate changes and human activities; (3) compared with the base period (1961–2004), the reduction of P was the leading cause of runoff reduction, with a contribution of 45.64%. The contribution of E0 and human activities to runoff changes are 13.91% and 40.45%, respectively.

Inconsistent hydrological frequency calculation and attribution analysis of annual runoff of Lancang river basin based on LWHM-LUCC model

<p>In the context of global climate change and intensive human activities, the runoff process in the Lancang River Basin has been greatly changed. This study proposed a lumped watershed hydrological model considering land use/cover change (LWHM-LUCC) for the frequency calculation and attribution analysis of annual runoff of Lancang River Basin from physical causes aspect. We first detected the variability of precipitation, evaporation, and runoff time series at annual time scale of the Lancang River Basin during 1961–2014 through the hydrological variation diagnosis system. Then, the inconsistent runoff frequency calculation method based on LWHM-LUCC model were applied to analyze the annual runoff frequency distribution in past, current and future period, respectively. Besides, the contribution rates of climate change and human activities on runoff variation were quantatively determined based on LWHM-LUCC model and scenarios simulation. The result showed that there was an abrupt increase of evaporation in 2002, and an abrupt decrease of runoff in 2004. From the distant past period, near past period, to the current period, the design runoff in the Lancang River Basin showed a declined trend, whereas the runoff in the current and future periods remained basically unchanged, and the difference between current and distant past period was much larger than that between current and near past period. The contribution rates of precipitation, evaporation, land use and other human activities to runoff variation were around 38%, 31%, 0% and 31%, respectively. This indicated climate change has greater impact on runoff variation than human activity in the Lancang River Basin.</p>

Drought and flood occurrences in the Lancang River Basin during the last 60 years: their variations and teleconnections with monsoons

Understanding the inconsistency in the effects of monsoon changes on drought and flood occurrences would allow scientists to identify useful indicators in the prediction and early warning of regional drought and flood. Based on the calculation of the Standardized Precipitation Index, monsoon indices, and water vapor fluxes from 1956 to 2015, the relationships between drought–flood occurrences and monsoons in different regions of the Lancang River Basin were investigated. Drought and flood occurrences had spatial differences. Areas located in the lower basin had high drought and flood occurrences. The frequencies of drought and flood occurrences have no obvious regional differences and mainly varied periodically at 3–5, 8–15, and 20–25 years. Because the impact and strength of the Tibetan Plateau Monsoon (TPM) and South Asian monsoon (SAM) are limited, the TPM and SAM are the key factors that affect the occurrences of drought and flood in the upstream and downstream regions of the Lancang River Basin, respectively. The TPM and SAM are potentially useful indicators in the prediction of drought and flood occurrences. These results are of great scientific merit in developing an effective mitigation strategy to reduce the impacts of drought–flood disasters in the Lancang River Basin.