Recent changes in extreme precipitation and drought over the Songhua River Basin, China, during 1960-2013

Based on ten indices of extreme precipitation and one drought index (composite index, Cl), the trends in extreme events were investigated using a Mann-Kendall non-parametric method at 39 stations in the Songhua River Basin (SHB) during 1960-2013. The regionally averaged wet-day precipitation (PRCPTOT) increased at a rate of 1.65 mm/year (R-2 = 0.28,P = 0.13), in which 82% of the stations experienced increases, but only 4 stations showed significant positive trends. The annual R95 and R99 exhibited slight upward trends at rates of 137 (R-2 = 0.21, P = 0.27) and 128 mm/year (R-2 = 0.23, P = 0.23) over the last 54 years; however, there were not significant trends in R95 and R99 at the 0.05 level. PRCPTOT, R95 and R99 showed similar spatial trends, in which positive trends mainly occurred in the northern and southeastern basins. The trends in the maximum 1-day precipitation (RX1day) and maximum 5-day precipitation (RX5day) do not show a prevalent trend (approximately 50% of the stations have a positive trend and the remaining stations have a negative trend). The simple daily intensity index (SDII) significantly decreased at an annual rate of 0.02 mm/d during 1960-2013 (R-2 = 0.66, P < 0.01); spatially, 49% of the stations experienced statistically significant decreases at the 0.05 level based on the Mann-Kendall non-parametric test. The regionally averaged heavy (R10mm) and very heavy precipitation days (R20mm) and consecutive wet days (CWD) showed no significant trends during the past 54 years; however, several individual extreme precipitation events, such as the flood of 1998 in the SHB, were well detected by these indices. The regionally averaged consecutive dry days (COD) significantly increased (R-2 = 0.79, P<0.01) at a rate of 0.22 days/year from 1960 to 2013. All of the stations exhibited statistically significant increases in CDD, excluding the Tongyu station in the western basin. The monthly RX5day values were highest in summer, from June to August, in the SHB; a peak occurred in July (67.5 mm) in the SHB during 1960-2013. The Cl peaked in July, with the highest value of 0.2 in the SHB during 1960-2013. However, the two lowest Cl values occurred in spring and fall, with values of -0.56 and -0.41, respectively. During April and May, when most of the spring drought events occur, a prevalent trend does not exist; moreover, almost no stations have statistically significant Cl increases. In August and September, respectively 79% and 97% of the stations exhibited a CI negative trend, but only 2 and 6 stations showed significant decreases at the 0.05 level. The increasing extreme climate events present a challenge for local water resources management. (C) 2015 Elsevier B.V. All rights reserved.