Spatial and temporal variation of precipitation during 1960-2015 in Northwestern China

Under the global climate change, research on the response characteristic of precipitation to climate change and its variation trend is of great significance. By employing the empirical orthogonal function (EOF), the TPFW-MK test and the PCD and PCP method, the multiple-time scale variability and spatial distribution of precipitation in different climate zones are studied by the monthly precipitation data from 122 meteorological stations in Northwestern China (NWC) during 1960-2015. The results indicated that the annual precipitation in 68% of the stations exhibited upward trends and the average annual precipitation increased at 2.6 mm per decade from 1960 to 2015. Opposite variation trends of annual precipitation were detected in different climate zones, significant positive trends in arid and semiarid zones, but negative trends in humid and semi-humid zones. Based on the Z-statistics by TPFW-MK test, winter precipitation exhibited a generally increasing trend, but the variation of summer precipitation showed remarkable regional differences. Mutation test indicated that middle 1980s was the major mutation point of precipitation series. According to the CDF plots, the proportion of precipitation between 0 and 300 mm decreased, while the proportion of precipitation more than 700 mm increased. The EOF analyses showed that the spatial distribution of precipitation had three typical modes, whole area consistent type, east-west opposite type and north-south opposite type. The greatest proportion of the whole area pattern revealed that the climate condition was controlled by some common factors despite the different variation trends. Trend analyses of PCD and PCP indicated that the inter-annual precipitation in about 77.3% of the stations had a high concentration degree, the unevenness of inter-annual precipitation distribution increased in humid and semi-humid zones and decreased in arid and semiarid zones, which was opposite to the variation trends of annual precipitation. Besides, the concentrate period of inter-annual precipitation had advanced over the last decades. The results will provide reliable references for addressing climate change, protecting ecological environment and preventing meteorological disasters.