Seasonal tropospheric cooling in Northeast China associated with cropland expansion

Abstract

Large-scale agricultural expansion can influence near-surface climate by altering surface energy fluxes, water, and albedo. It is less clear whether such effects extend through the full troposphere and how such effects vary in time. Here we use a novel dataset documenting the massive land use and land cover change due to agricultural expansion in Northeast China from 1982 to 2010 to assess how such expansion has influenced climate over the full troposphere. Confronting our land classification and climate data with a number of statistical approaches (linear regression, correlation analysis, Grangercausality), we find that cropland significantly increased by ∼28% over the near 30 year period in Northeast China-an average rate of nearly a percentage per year. This massive 30 year agricultural expansion is tightly associated with near-surface cooling identified in station data during the late growing season (August to September). Assuming no cropland expansion over the 30 year period, surface temperature would have increased by 0.93°C±0.4°C. Furthermore, the fingerprint of cropland-associated cooling extends upward into the atmospheric column, influencing the vertical structure of the regional troposphere and potentially its circulation. For every 10 percentage points increase in cropland fraction over Northeast China, regional full-troposphere temperature and geopotential height significantly decrease by 0.2°C-0.6°C and 20 m-80 m, respectively. These observed relationships are remarkably coherent across datasets, methodological choices, atmospheric levels, and theory, suggesting that the observational effects we identify are robust and imply the possibility of detectable land use change effects on regional circulation, with potential consequences for the East Asian monsoon.

Spatial and Temporal Variations in Extreme Precipitation and Temperature Events in the Beijing–Tianjin–Hebei Region of China over the Past Six Decades

“…This may be because irrigation is intense in the southern BTHR, and this has a significant cooling effect on the daily maximum temperature, which partially offsets the effect of urbanization [40]. Clearly, the cooling effects of cropland cannot be ignored [41]. At most stations, the daily minimum temperature and the indices of frequency of extreme cold weather events significantly increased and decreased, respectively.…”

Surface Temperature Trend Estimation over 12 Sites in Guinea Using 57 Years of Ground-Based Data

“…Pettorelli et al [86] highlighted that, NDVI in ecological studies has recently rapidly increased and its possible key role in future research of environmental change in an ecosystem context allows the better predictions of the effect of global warming, biodiversity reduction or habitat degradation. In fact, He et al [34] and Wang et al [87] found a positive correlation between the temperature and NDVI early and late in the growing season and a weak correlation in the mid-growing season in Kansas during the 1989-1997 period. Southern areas surrounding stations such as Kissidougou, Macenta and N'zerekore have stronger NDVI values, and the surface temperatures of these areas are less sensitive to the seasonal warming during March-April-May (MAM) compared to the rest of the country.…”

“…Some research works have analyzed these LCCs and their impacts on the climate, such as that of Mahmood et al [33], who studied the impacts of notable types of land cover changes, including agriculture, deforestation and afforestation, desertification and urbanization on the climate. In addition, the agricultural expansion influence on the climate over the full troposphere in Northeast China from 1982 to 2010 was studied by He et al [34].…”

Ecology and Climate of the Earth—The Same Biogeophysical System

“…For example, India monsoon precipitation is altered in response to changes in the surface fluxes from urbanization and, to some extent, the change of prevalent mixed forest into deciduous needle/leaf forest in Kerala [23]. As another example, there has been documentation of tropospheric cooling in northeast Asia due to cropland expansion [24].…”