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

Abstract

The effects of agricultural development on observed changes in near-surface atmospheric temperature and moisture from 1960 to 2014 over Northeast China are evaluated using data from 109 meteorological stations. Cultivated land fraction (CF) within a 3 km radius of the meteorological station is used as a quantitative indicator of agricultural intensity. Stations with large CFs experience a less significant increase in air temperature, especially in daily maximum temperature (Tmax) and a more rapid increase in vapor pressure (ea) and relative humidity (RH) than stations with small CFs, especially during the main growing season (from May to September). Compared with the reference station group withCF<0.2, cooling effects during May to September in terms of daily mean, maximum, and minimum temperature by −0.067°C, −0.081°C, and −0.069°C per decade and wetting effects of May to September regardingeaby 0.075 hPa and RH by 0.56% per decade exist for the station group withCF>0.5. The cooling and wetting effects can be attributed to the agricultural development and thus should be considered when analyzing the near-surface atmospheric temperature and moisture records in Northeast China.

Spatial and Temporal Variations of Compound Droughts and Hot Extremes in China

“…For example, it has been shown in previous studies that the cooling trend coexists with wetting trend in Central China (especially in the middle/lower reaches of the Yangtze River Valley) during summer, which may be linked to the warming trend in the sea surface temperature (SST) of the Indian Ocean that affects the interdecadal variability of the summer climate in China by changes in the Hadley circulation and subtropical high over the northwest Pacific [47][48][49]. Parts of Northeast China (i.e., Heilongjiang and Jilin province) also showed a decrease of compound extremes, which may partly result from the increase in precipitation (and the decrease in potential evaporation) and the cooling effect of agricultural irrigation [50,51] that affects the land atmospheric interaction. In general, Figure 3 shows increased compound droughts and hot extremes over most parts of China, highlighting the increased risk of extremes in these regions under global warming.…”

Seasonal tropospheric cooling in Northeast China associated with cropland expansion

“…albedo, soil moisture, surface roughness, and leaf area index) are crucial in determining regional climate (Field et al 2007, Lee and. Large alterations to the land surface, such as the conversion of grasslands to agricultural lands in Northeast Chia we analyze here, are thought to have their climate effects largely constrained to the nearsurface (Zhu et al 2012, Zhao et al 2016. Using a newly developed 29 year time-series of LULC data over Northeast China, we provide the first observational evidence that Northeast China's massive agricultural expansion (from 299 584 km 2 in 1982 to 382 400 km 2 in 2010) over the last ∼30 years has a climate influence that extends well beyond the surface.…”

“…Cropland expansion has been a powerful means to increase food security in China. At the same time, Northeast China has faced a number of droughts, resulting in increased irrigation water demands (Zhao et al 2016, Cong et al 2017, Yan et al 2018 and posing increased risks to regional water supplies. Future work should assess the robustness of our results using model experiments.…”

“…The climatology of China's daily and seasonal temperatures have been affected as well: in Xinjiang province in Northwest China, the warming trend in growing season daily average surface temperature among those stations adjacent to cultivation was smaller than those stations with little cultivated land nearby (Han and Yang 2013). In parts of Northeast China, a similar response has been documented, with the cooling effects of expanding irrigation (Kang and Eltahir 2019) being sufficiently large to dampen or fully-offset the warming signal from greenhouse gas emissions (Zhu et al 2012, Zhao et al 2016.…”

“…There is considerable evidence from both models and observations in other geographic contexts that cropland expansion (as well as intensification of irrigation and fertilization) can significantly impact climatological temperature, moisture, and circulation through biogeophysical and biogeochemical processes at the land-atmosphere interface (Mahmood et al 2006, Lobell et al 2008, Cook et al 2011, Lee et al 2011, Wei et al 2013, Zhao et al 2016. Intensified agriculture, for example, could serve to reduce surface air temperature by increasing energy partitioning towards latent, rather than sensible, heat Yang 2013, Zhang et al 2013).…”