Agricultural irrigation‐induced climatic effects: a case study in the middle and southern Loess Plateau area, China

Abstract

Irrigation and rain‐fed agriculture, the main agricultural practices in the middle and southern Loess Plateau area, impact the regional climate in different ways. Based on 38 meteorological stations in the middle and southern Loess Plateau area, the effects of agricultural irrigation on climatic variables from 1960 to 2005 were evaluated. Climatic trends from non‐irrigated areas were used as a reference. Trends in climatic variables for the growing season and the summer period are negatively correlated with the percentage of cultivated land within a 3 km radius of the meteorological stations. Trends for the average summer temperature (Ta), maximum temperature (Tmax), minimum temperature (Tmin) and the diurnal temperature range (DTR) decreased by 0.065, 0.073, 0.054 and 0.025 °C per decade, respectively. Summer net solar radiation (SR) decreased by 0.0325 MJ m−2 day−1 per decade and summer relative humidity (RH) increased by 0.255% per decade with a 10% increase in the area of cultivated land. The climatic effects on meteorological stations in irrigated areas are compared to the trends of non‐irrigated areas in the study region. The expansion of irrigation has had a noticeable cooling effect on summer Ta, Tmax, Tmin and DTR with values of 0.192, 0.193, 0.142 and 0.058 °C (10 years)−1, respectively. Irrigation increased RH by 0.916% per decade and net radiation reduced by 0.230 MJ m−2 day−1 per decade. On monthly scales, these effects were more obvious in June and August. The dependence of climatic trends on the proportion of cultivated land can be attributed to agricultural irrigation. The changes in climatic differences for Ta, Tmax, Tmin, RH and SR corresponded with the expansion of irrigation. The cooling effects induced by irrigation have also partly masked the effects of greenhouse gas‐induced warming.

Recent Trends of Extreme Precipitation and Their Teleconnection with Atmospheric Circulation in the Beijing-Tianjin Sand Source Region, China, 1960–2014

“…Trends for individual station data and regional series were estimated and the significance of the trends was determined using the Mann-Kendall test [40,41], which does not assume that data are normally distributed, and robustly responds to the effects of outliers in the series and has been widely used to test trends in hydrological and meteorological data [29,[42][43][44][45], and the 10% level of statistical significance was used. Sen's slope estimator was used to estimate the true slope of an existing trend (the change per year) [46].…”

Changes in reference evapotranspiration over the non‐monsoon region of China during 1961–2017: Relationships with atmospheric circulation and attributions

“…Some studies have proved that a primary dimming factor is air pollution and anthropogenic aerosols (Streets et al ., 2008; Ning et al ., 2016; Shi et al ., 2016; She et al ., 2017; Han et al ., 2018). Furthermore, changes in local climatic variables have been induced by agricultural activities, particularly irrigation (Han and Hu, 2012; Xu et al ., 2017). Agricultural irrigation affects climatic variables through cooling, wetting, and dimming, which changes the energy budget at the land–atmosphere interface (Han and Hu, 2012; Xu et al ., 2017).…”

“…Furthermore, changes in local climatic variables have been induced by agricultural activities, particularly irrigation (Han and Hu, 2012; Xu et al ., 2017). Agricultural irrigation affects climatic variables through cooling, wetting, and dimming, which changes the energy budget at the land–atmosphere interface (Han and Hu, 2012; Xu et al ., 2017). The change in the energy budget and increase in soil moisture accelerate evaporation and transpiration, which has increased air humidity in irrigation areas.…”

“…With more water being evaporated, water vapour can increase the cloud cover, which reduces R s reaching the earth's surface. This has been identified as a wetting, dimming, and cooling effect (Xu et al ., 2017). Previous research suggests that the near‐surface wind changes (including prior stilling and the recent reversal) is affected by changes in the surface roughness due to land use and cover change (LUCC) including afforestation and urbanization (Vautard et al ., 2010; Zhang et al ., 2014; Wu et al ., 2017b; Li et al ., 2017d; Li et al ., 2018).…”

Cooling and Wetting Effects of Agricultural Development on Near-Surface Atmosphere over Northeast China

“…The irrigated area in China increased from 30.1 × 10 6 ha in 1961 to 63.5 × 10 6 ha in 2013, with more rapidly expansion in the northern region. Meanwhile, the effects of irrigation on climate have been investigated over Northern China: from the arid Northwest region [7,31] and the Yellow River Basin [32,33] to the Huang-Huai-Hai Plain [34,35]. As a main agricultural area in China, Northeast China has undergone rapid cropland extension in the last century, where the cropland area increased from 9.8% of Northeast China area in 1908 to 29.6% in 2000 [36].…”