Determining the impact of a severe dry to wet transition on watershed hydrodynamics in California, USA with an integrated hydrologic model

Hydrol. Earth Syst. Sci.

Vahmani

2020

Self Cite

Abstract. Projecting the spatiotemporal changes in water resources under a no-analog future climate requires physically based integrated hydrologic models which simulate the transfer of water and energy across the earth's surface. These models show promise in the context of unprecedented climate extremes given their reliance on the underlying physics of the system as opposed to empirical relationships. However, these techniques are plagued by several sources of uncertainty, including the inaccuracy of input datasets such as meteorological forcing. These datasets, usually derived from climate models or satellite-based products, are typically only resolved on the order of tens to hundreds of kilometers, while hydrologic variables of interest (e.g., discharge and groundwater levels) require a resolution at much smaller scales. In this work, a high-resolution hydrologic model is forced with various resolutions of meteorological forcing (0.5 to 40.5 km) generated by a dynamical downscaling analysis from the regional climate model Weather Research and Forecasting (WRF). The Cosumnes watershed, which spans the Sierra Nevada and Central Valley interface of California (USA), exhibits semi-natural flow conditions due to its rare undammed river basin and is used here as a test bed to illustrate potential impacts of various resolutions of meteorological forcing on snow accumulation and snowmelt, surface runoff, infiltration, evapotranspiration, and groundwater levels. Results show that the errors in spatial distribution patterns impact land surface processes and can be delayed in time. Localized biases in groundwater levels can be as large as 5–10 m and 3 m in surface water. Most hydrologic variables reveal that biases are seasonally and spatially dependent, which can have serious implications for model calibration and ultimately water management decisions.

Section: Numerical-modeling Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity of meteorological-forcing resolution on hydrologic variables

Hydrol. Earth Syst. Sci.

Vahmani

2020

Self Cite

“…The Cosumnes River is one of the last rivers in the western United States without a major dam, offering a rare opportunity to isolate the impacts of a changing climate on the hydrodynamics without reservoir management consideration (Maina et al, 2020a;Maina and SiirilaWoodburn, 2020 important aspects of the large-scale hydrology patterns of the state, namely the assessment of interactions between changes in precipitation, snowpack, streamflow, and groundwater across elevation and geologic gradients. Located in Northern California, USA, the Cosumnes watershed is approximately 7,000 km 2 in size (Figure 1) and is between the American and the Mokelumne Rivers.…”

Section: The Cosumnes Watershedmentioning

confidence: 99%

“…More information about the coupling between ParFlow and CLM can be found in Maxwell & Miller, (2005). CLM uses the following outputs of the VR-CESM model at 3-hourly resolution to solve the energy balance at the land surface: precipitation, air temperature, specific humidity, m and the land surface through a multi-year time period (Maina et al, 2020a). Therefore, to be conservative for imposing the lower boundary layer, anything below 80 m is expected to remain fully saturated.…”

Section: Integrated Hydrologic Model: Parflow-clmmentioning

confidence: 99%

Projecting the impacts of end of century climate extremes on the hydrology in California

Rhoades

et al. 2021

Preprint

Self Cite

Abstract. In California, it is essential to understand the evolution of water resources in response to a changing climate to sustain its economy and agriculture and build resilient communities. Although extreme conditions have characterized the historical hydroclimate of California, climate change will likely intensify hydroclimatic extremes by the End of Century (EoC). However, few studies have investigated the impacts of EoC extremes on watershed hydrology. We use cutting-edge global climate and integrated hydrologic models to simulate EoC extremes and their effects on the water-energy balance. We assess the impacts of projected driest, median, and wettest water years under a Representative Concentration Pathway (RCP) 8.5 on the hydrodynamics of the Cosumnes river basin. High temperatures (> 2.5 °C) and precipitation (> 38 %) will characterize the EoC extreme water years compared to their historical counterparts. Also, precipitation, mostly in the form of rain, is projected to fall earlier. This change reduces snowpack by more than 90 %, increases peak surface water and groundwater storages up to 75 % and 23 %, respectively, and makes these peak storages occur earlier in the year. Because EoC temperatures and soil moisture are high, both potential and actual evapotranspiration (ET) increase. The latter, along with the lack of snowmelt in the warm EoC, cause surface water and groundwater storages to significantly decrease in summer, with groundwater showing the highest rates of decrease. Besides, the changes in the precipitation phase lead the lower-order streams to dry out in EoC summer whereas the mainstream experiences an increase in storage.

“…Land use and land cover (LULC) was chosen to be heterogeneous and is based on the real‐world spatial distribution of a region located near the city of Sacramento in northern California, USA. This region was selected given its heterogeneous distribution of different LULC types, typical of many mixed‐land environments, including wetland, cultivated lands, pasture, grasslands, and open space (Maina et al, 2020; Maina & Siirila‐Woodburn, 2019). The northern section of the model was homogeneously classified as evergreen forestland to provide additional insights into this LULC environment (see Figure 1).…”

Section: Numerical Set‐upmentioning

confidence: 99%

The Role of Subsurface Flow on Evapotranspiration: A Global Sensitivity Analysis

Water Resources Research

2020

Water resources are impacted by water‐energy balance fluxes at the land surface, most notably evapotranspiration (ET), the largest component of surface energy balance. While integrated hydrologic models show promise in quantifying the nonlinear dynamics at this interface, the model results are plagued by parametric uncertainties. Given the high computational demand of running multiple parameter spaces of these models, little is known about how these uncertainties propagate into land surface processes. In this work, we perform a global sensitivity analysis by computing Sobol and AMAE indices using a surrogate model constructed with a polynomial chaos expansion to assess the impacts of the subsurface physical properties on ET. We do so by modeling a semisynthetic test case. Our results show that the effects of vertical hydraulic conductivity, porosity, and the water retention curve parameter Van Genuchten α mainly control ET. However, we note that while evaporation (E) shows behavior similar to the ET with high sensitivity to the parameters controlling the flow in the unsaturated zone, transpiration (T) is very sensitive to the saturated zone parameters and groundwater flow, especially during periods without rain. Our results also show that heterogeneities in land cover impact the flow in the saturated zone. Furthermore, our work demonstrates that reduced‐order models can be developed to make integrated models more accessible for rigorous sensitivity analyses and calibration purposes.