Impacts of land use and land cover change on urban hydroclimate of Colorado River Basin

Rapid urbanization and population growth occurring in the cities of South Western

United States have led to significant modifications in its environment at local and

regional scales. Both local and regional climate changes are expected to have massive

impacts on the hydrology of Colorado River Basin (CRB), thereby accentuating the need

of study of hydro-climatic impacts on water resource management in this region. This

thesis is devoted to understanding the impact of land use and land cover (LULC) changes

on the local and regional hydroclimate, with the goal to address urban planning issues

and provide guidance for sustainable development.

In this study, three densely populated urban areas, viz. Phoenix, Las Vegas and

Denver in the CRB are selected to capture the various dimensions of the impacts of land

use changes on the regional hydroclimate in the entire CRB. Weather Research and

Forecast (WRF) model, incorporating the latest urban modeling system, is adopted for

regional climate modeling. Two major types of urban LULC changes are studied in this

Thesis: (1) incorporation of urban trees with their radiative cooling effect, tested in

Phoenix metropolitan, and (2) projected urban expansion in 2100 obtained from

Integrated Climate and Land Use Scenarios (ICLUS) developed by the US

Environmental Protection Agency for all three cities.

The results demonstrated prominent nocturnal cooling effect of due to radiative

shading effect of the urban trees for Phoenix reducing urban surface and air temperature

by about 2~9 °C and 1~5 °C respectively and increasing relative humidity by 10~20%

during an mean diurnal cycle. The simulations of urban growth in CRB demonstratedii

nocturnal warming of about 0.36 °C, 1.07 °C, and 0.94 °C 2m-air temperature and

comparatively insignificant change in daytime temperature, with the thermal environment

of Denver being the most sensitive the urban growth. The urban hydroclimatic study

carried out in the thesis assists in identifying both context specific and generalizable

relationships, patterns among the cities, and is expected to facilitate urban planning and

management in local (cities) and regional scales.