Spatial distribution and temporal variation of reference evapotranspiration in the Three Gorges Reservoir area during 1960–2013

Monitoring the spatial distribution of reference evapotranspiration (ET0) and quantifying temporal variations offer valuable information about hydrology, irrigation water requirements and water resources management. Under climate warming and Three Gorges Reservoir (TGR) impoundment conditions, it is critical to survey the ET0 variation in the Three Gorges Reservoir area (TGRA) China. Temporal and spatial patterns in ET0 over the TGRA were investigated for the period 1960-2013, based on daily data from 41 meteorological stations. The Mann-Kendall test and Sen's slope estimator were used to examine ET0 trend. The presence of abrupt changes was checked using the Pettitt test, moving t-test (MTT) and cumulative sum (CUSUM) method. The spatial distribution of the mean annual ET0 in the TGRA for 1960-2013 shows an east-west gradient structure with low ET0 in the area south of the TGR (STGR) and high ET0 in the area downstream of TGR (DTGR). The spatial distribution for post-dam period is similar to that for 1960-2013. Abrupt changes of annual ET0 over the TGRA occurred in 1982. These changes were mainly related to climate warming in TGRA during the 1980s. ET0 in the region exhibited an obvious decreasing trend until the early 1980s (1982), at a rate of -1.41mma(-1). However, the downward trend reversed in 1982, followed by a rate of increase of 1.11mma(-1). For the whole period of 1960-2013, the overall decreasing trend in TGRA was mainly due to downward trend in 1960-1982. During the post-dam period, the upward trends are still more pronounced. The TGR may have some effects on ET0 at stations that lie in or near the Three Gorges Dam (TGD) in some cases. However, there is no evidence to indicate that the TGD would affect other locations. In general, ET0 variation is more related to climate change rather than dam-related changes.