Temporal characteristics of evaporation trends and their attribution to
meteorological drivers in Roorkee (India)
Abstract
Pan evaporation is an important indicator of atmospheric evaporative
demand, and its long-term variation is of much concern in studies of
climate change. Estimation of evaporation is also important for water
budgeting and yet is difficult to quantify because of the combined
effects of four meteorological variables: net radiation, wind speed,
atmospheric humidity, and air temperature. This work considered the
temporal trends of pan evaporation and the meteorological variables that
affect them for a station located in Roorkee (India). In this study,
observed meteorological data at NIH observatory for the period from 1987
to 2018 was used for trend analysis of the data (rainfall, relative
humidity, maximum temperature, minimum temperature, average temperature,
wind speed and pan evaporation). Evaporation was also estimated using
Penman method, Meyer method and other empirical equations, and compared
with the observed evaporation values. Anomalies in the time series of
meteorological variables were computed to find out the magnitude of rise
or fall in the series. Pettitt-Mann-Whitney (PMW) test for detection of
shift in the time series has been carried out, and the trend and shift
in meteorological data is correlated with the same in evaporation. Based
on this research, a number of conclusions are drawn: (1) minimum
temperature and relative humidity have been increasing whereas maximum
temperature and wind speed have been decreasing during the period
1987-2018, (2) pan evaporation series has not shown any significant
trend, except during post-monsoon when it decreased, (3) significant
change points (shifts) in the time series of temperature, relative
humidity and wind speed may attribute the influence of fast urbanization
and enhanced anthropogenic activities in Roorkee town after creation of
Uttarakhand as a separate State in the year 2000.