Abstract
To analyze extreme climatic change features and effects on runoff in the Manas River basin, Xinjiang, data were collected including daily mean temperature, daily highest and lowest temperatures, and daily precipitation from six meteorological stations in the Manas River basin as well as daily runoff data from the Kensiwate hydrologic stations during 1960-2010. By adopting the threshold value of extreme climatic events defined by ET ALDDMI and with the aid of nonparametric statistical tests, Pearson III methods, and others, the effect of extreme climatic events on extreme runoff in the past 50 years in the Manas River basin, Xinjiang, was analyzed. The results showed that in the past 50 years, 1) extreme warming events (annual extreme maximum temperature, warm-day and warm-night index) have risen significantly (P < 0.05). Among these the warm-day and warm-night indices decreased abruptly in 2001 and 1996, respectively. With respect to extreme cold events (annual extreme minimum temperature, cold-day and cold-night indices), the extreme minimum temperature was high after 1976, and the cold-day index weakened significantly, similar to the cold-night index. 2) Except for the continuous drought days (CDD), the other five indices of extreme precipitation events appeared to trend upward, with an abrupt change around 1993. 3) Flood events in 1990, mostly in summer, accounted for 42.9% of the total number of floods since 1960. Floods increased mainly because extremely high summer temperatures increased snowmelt, increasing inflow to the rivers, which combined with more precipitation to cause the increase in summer peak flood discharge.
Highlights
Many studies have demonstrated that extreme climatic events, such as floods, droughts, typhoons, high temperatures, low temperatures, rain, snow, freezes, and so on, seriously affect social stability, economic development, and national well-being [1]
Manas River basin locates at the joint of northern foot of Tianshan Mountain and south brim of Junggar Basin
Using SPSS 17.0, we analyzed extreme temperature, precipitation, and extreme runoff, and the correlation coefficients of maximum peak discharge with monthly maximum precipitation, simple precipitation intensity, annual maximum runoff volume, and summer high temperature of 0.483, 0.562, 0.804, and 0.756, respectively. These results indicate that floods have been increasing in the Manas River basin mainly because of increasing precipitation and increased ice- and snowmelt, caused by increasing high temperatures in summer
Summary
Many studies have demonstrated that extreme climatic events, such as floods, droughts, typhoons, high temperatures, low temperatures, rain, snow, freezes, and so on, seriously affect social stability, economic development, and national well-being [1]. Climatic change is likely to alter the current global hydrologic cycle, resulting in increasing frequency and strength of extreme climatic events [2], presenting a serious threat to global and regional water security and a significant challenge to the survival of mankind and sustainable social development [3]. These influences, are different in both space and time due to spatial and temporal variations of temperature changes [4] [5]. Study of extreme climatic events and impact on extreme runoff will be very significant for mitigating disasters and damages and promoting regional water security
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