Most land surface models (LSMs) do not explicitly represent surface ponding, infiltration of ponded water, or the soil macropore effects on infiltration, percolation, and groundwater recharge. In this study, we implement a dual-permeability model (DPM) based on the mixed-form Richards’ equation, which solves pressure head continuously across unsaturated and saturated zones while conserves mass, into the Noah-MP LSM to represent slow flow through soil matrix and rapid flow through macropore networks. The model explicitly computes surface ponding depth, infiltration of ponded water, and runoff beyond a ponding threshold (infiltration-excess runoff) by switching the atmospheric boundary condition between head and flux boundary conditions. The new model also provides two optional soil water retention models of Van Genuchten (VG) and Brooks-Corey (BC). Model experiments over the conterminous US indicate that 1) surface ponded water and its runoff contribute substantially to seasonal variations in total water storage and peak flows in wet regions with low soil permeability (e.g., the Lower Mississippi River and surrounding regions), 2) the VG model produces drier topsoil with less soil surface evaporation than does the BC model with the Clapp-Hornberger parameters, especially during droughts and in dry regions, better matching remote sensing soil moisture, and 3) DMP produces more runoff with increased subsurface runoff, thereby improving the modeling skill at monthly scale over all subbasins of the Mississippi River, especially for low flow events. This study also highlights the importance of consistent representations of soil and plant hydraulics in Earth System Models to modeling ecosystem drought resilience.

Early peopling of Brazil’s Northeast region (BRN) took place under an intimate relationship between humans and water scarcity, as the region, especially the state of Ceará (CE), has dealt historically with severe drought events since the 1800’s, which commonly led to catastrophic impacts of mass migration and deaths of thousands of people. Throughout the last century, the so-called “Droughts Polygon” region experienced intense infrastructural development, with the expansion of a dense network of reservoirs. This resulted in the evolution of a complex hydrologic system requiring a holistic investigation in terms of its hydrologic tradeoffs. This paper presents a parsimonious hydrologic modeling approach to investigate the 100-year (1920-2020) evolution of a dense surface-water network in the 24,500 km² Upper Jaguaribe Basin, with the ultimate goal of generating insights into the coevolution of a tightly coupled human-water system. Our model is driven by both climatic and human inputs, while model structure is allowed to evolve over time to dynamically mimic evolution of population size, reservoir count and water demand. Hundred years of continuous growth in storage capacity experienced within the UJ Basin is found to reflect the transition from complete vulnerability to droughts to achievement of significantly increased levels of water security. However, drought severity had in the meantime disproportionally intensified in this period, especially in reservoirs of medium to small capacities. Our analysis results have generated valuable insights into the different roles that reservoir expansion has played in securing the stability of human settlement patterns in drought prone regions.