Modeling of the effects of land-use change and irrigation on local climate

Jiming Jin, Norman L. Miller, Bo Yang

Research output: Chapter in Book/Report/Conference proceedingChapter

1 Scopus citations

Abstract

In this chapter, the effects of land-use change and irrigation on local climate are quantified using the Pennsylvania State University/National Center for Atmospheric Research (NCAR) fifth generation Mesoscale Model (MM5) coupled with the Community Land Model version 3 (CLM3). We chose the Central Valley in California as an example. The simulations for this region were forced with modern-day and presettlement land-use types at 30-km spatial resolution for the period 1 October 1995 to 30 September 1996. This study shows that land-use change has significantly altered the structure of the planetary boundary layer (PBL) that affects near-surface temperature, which is different from many other land-use change studies indicating that albedo and evapotranspiration variations are the key processes influencing climate at local-toregional scales. Our modeling results show that modern-day daily maximum near-surface air temperature (Tmax) has decreased due to agricultural expansion since presettlement. This decrease is caused by weaker sensible heat flux resulting from the lower surface roughness lengths associated with modern-day crops. The lower roughness lengths in the Central Valley also result in stronger winds that lead to a higher PBL. The higher PBL produces stronger sensible heat flux, causing nighttime warming. In addition to land-use change, cropland irrigation has also affected hydroclimate processes within the Central Valley. We generated a 10-member MM5-CLM3 ensemble simulation, where each ensemble member was forced by a fixed volumetric soil water content (SWC) between 3% and 30%, at 3% intervals, over the irrigated areas during a spring-summer growing season, 1 March to 31 August 1996. The results show that irrigation lowers the modern day cropland surface temperature. Daytime cooling is produced by irrigation-related evaporation enhancement. This increased evaporation also dominates the nighttime surface cooling process. Surface cooling and the resulting weaker sensible heat flux further lower the near-surface air temperature. Thus, irrigation strengthens the daytime near-surface air temperature reduction that is caused by land-use change, and a similar temperature change is seen for observations over irrigated cropland. Based on our modeling results, the nighttime near-surface warming induced by land-use change is alleviated by low-intensity irrigation (17%<SWC<19%), but such warming completely reverses to a cooling effect under high-intensity irrigation (SWC>19%). The land-use changes discussed in this study are commonly observed in many regions of the world, and the physical processes identified here can be used to better understand temperature variations over other areas with similar land-use changes.

Original languageEnglish (US)
Title of host publicationLand Use
Subtitle of host publicationPlanning, Regulations, and Environment
PublisherNova Science Publishers, Inc.
Pages125-147
Number of pages23
ISBN (Print)9781622573578
StatePublished - Oct 2012
Externally publishedYes

ASJC Scopus subject areas

  • General Environmental Science
  • General Social Sciences

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