| dc.description.abstract | Drought events have accelerated and intensified in recent decades. In the 21st century, the
number and duration of severe drought events are expected to increase even further. The impact
on crops and natural vegetation has already become more pronounced over the last years, as crop
yield losses increase and forest fires become more frequent. This creates increasing pressure on
water demand and food security globally. Therefore, it is important to understand not only the
impact of droughts on vegetation but also the regeneration of vegetation in post-drought periods.
In this study, vegetation regeneration rates in Nebraska (United States) are determined using
the Standardized Precipitation Evapotranspiration Index (SPEI) and the Enhanced Vegetation
Index (EVI). The results show that the correlation coefficient between the SPEI and EVI is
generally high for grassland (0.8 - 1.0) and low for cropland (∼ 0.2). The time shift, days
between the two datasets at the highest possible correlation coefficient, is between 75 and 125
days for grassland which is mainly dependent on the local topography which is the main driver
of groundwater flow and therefore hydraulic gradients in the area. Various factors, including the
water table, rooting depth, groundwater recharge delay, recharge area, local depressions filled
with water, as well as soil moisture, contribute to deviations in time shifts and recovery times
within the study area. The average recovery time of grassland is approximately 3.97 months
(121 days), while for cropland it is 3.64 months (111 days). The drought timing is shown to
be important in the recovery time. The later a drought ends in the growing season, the longer
the vegetation regeneration time. Between the drought time or intensity and the vegetation
regeneration time, no significant correlation was found, as soil moisture presumably dominates
the drought recovery time. The results of this study provide insight into the vegetation recovery
time of both grassland and cropland. Understanding these dynamics is crucial for enhancing
large-scale hydrological models, such as PCR-GLOBWB 2.0, by incorporating accurate estimates
of vegetation water demands during post-drought periods. As soil moisture is projected to
decline further in the future, this research highlights the significance of acknowledging extended
periods for drought recovery, thereby contributing to a more comprehensive assessment of the
potential impacts of drought on vegetation regeneration for better sustainable water resource
management. | |
