Abstract:
Drought monitoring is a key to planning, vulnerability and impact assessment, forwarding adaptation and
mitigation options, and predicting its occurrences, frequency, and severity levels. This study aimed to
monitor agro-meteorological drought conditions using geospatial technology in Menna Watershed,
Northwestern Ethiopia. The study used Climate Hazard Group InfraRed Precipitation with Stations
(CHIRPS) rainfall data, two Moderate Resolution Imaging Spectro-radiometer (MODIS) datasets
(MOD13Q1 and MOD11A2), meteorological station data and Crop yield data. Meteorological station
rainfall data was used to evaluate the performance of the CHIRPS rainfall data. The CHIRPS
dataset was used to characterize meteorological drought, determine the onset, cessation, and
length of the rainy season and to analyze climate extreme indices. Mann–Kendall (MK) test and Sen’s
slope estimator were employed to detect the rainfall trends and magnitude of change, respectively.
Coefficient of variation (CV) was used to analyze variability of rainfall. In addition, the percent of
normal (PN), standardized anomaly index (SAI), and standardized precipitation index (SPI) were
computed from the CHIRPS rainfall. Normalized Difference Vegetation Index (NDVI), Vegetation
Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI) were
employed during the crop growing seasons from 2000 to 2022 to characterize agricultural drought. The
performance evaluation result of the study revealed that there was a good agreement between the
station and CHIRPS rainfall data (R2=0.88). The result of MK and Sen’s slope trend test shows
that the Kiremt season has an insignificant decreasing trend while annual and Belg registered a
significant increasing trend. The study also reveals that the highland and upper highland part of
the study area was characterized as having a longer length of rainy season, whereas, lowland and
midland zones have shorter lengths of rainy season. In addition, the computed extreme
temperature indices revealed that significant decrease in the number of cold days and nights, and
an increase in the number of warm days and nights. Conversely, extreme rainfall indices showed
a decreasing trend throughout the study area. The spatiotemporal distribution of meteorological
and agricultural drought reveals that during 2009 and 2015 the area was extensively hit by
drought while 2001 and 2007 were wet years with good crop yields. The frequency of agro meteorological drought occurrence ranges from 0-22 times in the last 23 years. The lowland and
midland parts of the study area were frequently affected by droughts. The combined drought-prone
area map also showed that 15.1% and 82.8% of the study area were vulnerable to moderate and
slight droughts, respectively. Thus, the Menna watershed, as a drought-prone area, has frequently
been affected by recurrent droughts, which needs regular drought monitoring. Therefore, the
community in the study area should be assisted by an improved early warning system and
introduce quick-mature and drought-resistant crops.