Seasonal effects of irrigation on land–atmosphere latent heat, sensible heat, and carbon fluxes in semiarid basin

Abstract

Abstract. Irrigation, which constitutes ∼ 70 % of the total amount of freshwater consumed by the human population, is significantly impacting land-atmosphere fluxes. In this study, using the improved Community Land Model version 4.5 (CLM4.5) with an active crop model, two high-resolution (∼ 1 km) simulations investigating the effects of irrigation on latent heat (LH), sensible heat (SH), and carbon fluxes (or net ecosystem exchange, NEE) from land to atmosphere in the Heihe River basin in northwestern China were conducted using a high-quality irrigation dataset compiled from 1981 to 2013. The model output and measurements from remote sensing demonstrated the capacity of the developed models to reproduce ecological and hydrological processes. The results revealed that the effects of irrigation on LH and SH are strongest during summer, with a LH increase of ∼ 100 W m −2 and a SH decrease of ∼ 60 W m −2 over intensely irrigated areas. However, the reactions are much weaker during spring and autumn when there is much less irrigation. When the irrigation rate is below 5 mm day −1 , the LH generally increases, whereas the SH decreases with growing irrigation rates. However, when the irrigation threshold is in excess of 5 mm day −1 , there is no accrued effect of irrigation on the LH and SH. Irrigation produces opposite effects to the NEE during spring and summer. During the spring, irrigation yields more discharged carbon from the land to the atmosphere, increasing the NEE value by 0.4-0.8 gC m −2 day −1 , while the summer irrigation favors crop fixing of carbon from atmospheric CO 2 , decreasing the NEE value by ∼ 0.8 gC m −2 day −1 . The repercussions of irrigation on land-atmosphere fluxes are not solely linked to the irrigation amount, and other parameters (especially the temperature) also control the effects of irrigation on LH, SH, and NEE.

A High‐Resolution Land Model With Groundwater Lateral Flow, Water Use, and Soil Freeze‐Thaw Front Dynamics and its Applications in an Endorheic Basin

“…On the contrary, the data from Wang () were based on high‐resolution observations and field surveys in China and are more appropriate for the permafrost research in some regions of China, such as HRB. In general, based on the validations in this study that supplemented previous tests (Zeng, Xie, Yu, Liu, Wang, Jia, et al, ; Zeng, Xie, Yu, Liu, Wang, Zou, et al, ; Zeng, Xie, & Liu, ), CAS‐LSM can be considered as a satisfactory tool for studying land processes, especially in cold and arid regions experiencing intensive human activity.…”

“…A scheme of HWR was incorporated into CLM4.5 as a submodel (Zeng, Xie, & Liu, ; Zou et al, ). Water withdrawal is classified as GW pumping and surface water intake.…”

“…The soil data set included in the CLM4.5 model was replaced with the China Soil Characteristics Dataset with a 1‐km resolution (Dai et al, ). We used the 1‐km monthly irrigation data sets (from both GW and river water) as the model input, provided by the Cold and Arid Regions Science Data Center at Lanzhou (Zeng, Xie, & Liu, ). These data were developed based on the local statistical data from a water resources bulletin, which reflects the actual water consumption in the study area.…”

“…Zeng, Xie, Yu, Liu, Wang, Zou, et al () introduced a scheme of GLF into a community land model (CLM) and better reproduced the spatial pattern of GW depth at both river and basin scales. GW dynamics is often linked with human water regulation (HWR; Pokhrel et al, ; Xie et al, ; Yao et al, ; Zeng, Xie, & Liu, ; Zeng, Xie, & Zou, ). In addition, the changes in depth of frost and thaw fronts (FTFs) can be regarded as an important climatic and environmental indicator (Frauenfeld et al, ; Yi et al, ).…”

Contributions of climate change and groundwater extraction to soil moisture trends

“…Soil drying could increase the possibility of agricultural drought and fire (Dai, 2011), and it affects plant transpiration, photosynthesis, microbial activity, and a number of biogeochemical processes. Significant decreasing trends in soil moisture can lead to water scarcity, threatening the water supply and associated food production (Döll et al, 2009;Wisser et al, 2010;Albergel et al, 2012;Wada et al, 2013;Dai, 2013;Zhan et al, 2016). Soil moisture trends are affected by both climate (e.g., precipitation and temperature) and human activities (e.g., groundwater (GW) extraction).…”