Abstract. Dryland regions are characterised by water scarcity and are facing
major challenges under climate change. One difficulty is anticipating how
rainfall will be partitioned into evaporative losses, groundwater, soil
moisture, and runoff (the water balance) in the future, which has important
implications for water resources and dryland ecosystems. However, in order
to effectively estimate the water balance, hydrological models in drylands
need to capture the key processes at the appropriate spatio-temporal scales.
These include spatially restricted and temporally brief rainfall, high
evaporation rates, transmission losses, and focused groundwater recharge.
Lack of available input and evaluation data and the high computational costs
of explicit representation of ephemeral surface–groundwater interactions
restrict the usefulness of most hydrological models in these environments.
Therefore, here we have developed a parsimonious distributed hydrological
model for DRYland Partitioning (DRYP). The DRYP model incorporates the key
processes of water partitioning in dryland regions with limited data
requirements, and we tested it in the data-rich Walnut Gulch Experimental
Watershed against measurements of streamflow, soil moisture, and
evapotranspiration. Overall, DRYP showed skill in quantifying the main
components of the dryland water balance including monthly observations of
streamflow (Nash–Sutcliffe efficiency, NSE, ∼ 0.7),
evapotranspiration (NSE > 0.6), and soil moisture (NSE ∼ 0.7). The model showed that evapotranspiration consumes > 90 % of the total precipitation input to the catchment and
that < 1 % leaves the catchment as streamflow. Greater than 90 % of the overland flow generated in the catchment is lost through
ephemeral channels as transmission losses. However, only ∼ 35 % of the total transmission losses percolate to the groundwater aquifer
as focused groundwater recharge, whereas the rest is lost to the atmosphere
as riparian evapotranspiration. Overall, DRYP is a modular, versatile, and
parsimonious Python-based model which can be used to anticipate and plan for
climatic and anthropogenic changes to water fluxes and storage in dryland
regions.
DRYP 1.0: a parsimonious hydrological model of DRYland Partitioning of the water balance
