Publications

Allen, MA; Roberts, DA; McFadden, JP (2021). Reduced urban green cover and daytime cooling capacity during the 2012-2016 California drought. URBAN CLIMATE, 36, 100768.

Abstract
Urban vegetation mitigates elevated temperatures in cities. Drought presents an important challenge to urban heat mitigation as prolonged dry periods cause reduced evapotranspiration and losses of green vegetation cover. To measure drought impacts on the urban environment and climate, we used visible short-wave infrared satellite imagery acquired throughout the 2012-16 drought in California to quantify effects on fractional vegetation cover in the Los Angeles urbanized region. We then used satellite thermal imagery with repeat high-resolution airborne thermal imagery to measure how drought-induced reductions of green vegetation cover affected urban land surface temperature (LST) and the cooling effect of urban vegetation. Green vegetation cover declined from 29.3% in 2011 to 24.6% in 2016 in urban Los Angeles County. Over the drought, the annual mean daytime LST increased from 34.4 degrees C in 2010 to 37.1 degrees C in 2014. Despite the large-scale homogenization of LST, tree- and grass-dominated areas differed in how they were affected by the drought, with larger losses of vegetation fractional cover and stronger reductions in cooling effect for grass compared to tree-covered areas due to different plant physiological responses and irrigation changes. Results suggest that drought presents a challenge to urban resiliency, as vegetation is often a main component of heat mitigation plans.

DOI:
10.1016/j.uclim.2020.100768

ISSN:
2212-0955