Quantifying the Impact of Excess Moisture From Transpiration From Crops on an Extreme Heat Wave Event in the Midwestern U.S.: A Top‐Down Constraint From Moderate Resolution Imaging Spectroradiometer Water Vapor Retrieval

Abstract

The primary focus of this study is to understand the contribution from excess moisture from crop transpiration to the severity of a heat wave episode that hit the Midwestern U.S. from 16 to 20 July 2011. To elucidate this, we first provide an optimal estimate of the transpiration water vapor flux using satellite total column water vapor retrievals whose accuracy and precision are characterized using independent observations. The posterior transpiration flux is estimated using a local ensemble transform Kalman filter that employs a mesoscale weather model as the forward model. The new estimation suggests that the prior values of transpiration flux from crops are biased high by 15%. We further use the constrained flux to examine the sensitivity of meteorology to the contributions from crops. Over the agricultural areas during daytime, elevated moisture (up to 40%) from crops not only increases humidity (thus the heat index) but also provides a positive radiative forcing by increasing downward longwave radiation (13 ± 4 W m−2) that results in even higher surface air temperature (+0.4 °C). Consequently, we find that the elevated moisture generally provides positive feedback to aggravate the heat wave, with daytime enhancements of heat index by as large as 3.3 ± 0.8 °C. Due to a strong diurnal cycle in the transpiration, the feedback tends to be stronger in the afternoon (up to 5 °C) and weaker at night. Results offer a potential basis for designing mitigation strategies for the effect of transpiration from agriculture in the future, in addition to improving the estimation of canopy transpiration.

Impact Forecasting to Support Emergency Management of Natural Hazards

“…Although drought and heat waves exhibit similar meteorological drivers, they are associated with different impacts: while droughts lead to agricultural yield losses, limitations in water supply, water quality and hydropower (Ding et al, 2011;Stahl et al, 2016), wildfires and loss of lives (Turco et al, 2018), heat waves impact human mortality or morbidity (typically cardiovascular or respiratory, Arbuthnott & Hajat, 2017;de' Donato et al, 2015;Ekamper et al, 2010), work productivity (Ciuha et al, 2019), and agriculture (Parker et al, 2020;Souri et al, 2020). Droughts often have secondary impacts whereby outputs from one industry/sector become inputs into other industries/sectors.…”

Distinct Impacts of Land Use and Land Management on Summer Temperatures

“…Observation-based studies suggest a nighttime warming in irrigated areas (Kanamaru and Kanamitsu, 2008;Chen and Jeong, 2018) because irrigation increases soil heat capacity (Kalnay and Cai, 2003) and thermal conductivity (Kanamaru and Kanamitsu, 2008), which allows more heat to be stored during daytime and released from the ground to the air during nighttime. Meanwhile, elevated moisture of the air would enhance downward longwave radiation, which would have a warming effect especially during night (Souri et al, 2020). In our results, although increased ground heat flux (implying more heat entered into the soil) is evident in the irrigated areas during daytime (Figure 4F), decreased ground heat flux (implying more heat released from the ground) is not found during nighttime (Figure 5F), and irrigation leads to a slight cooling in daily minimum temperature (Figures 3F,H).…”