Whats new in RHESSys (Regional Hydro-Ecological Simulation System)

Posted May 11, 2022

A Hydroinformatics Blog Post
Organized by the CUAHSI Informatics Standing Committee. Contributions are welcome, please contact Veronica Sosa Gonzalez at email hidden; JavaScript is required.

By: Naomi Tague, University of California, Santa Barbara

RHESSys is a hydro-ecologic model that has been used in a wide range of modeling applications including estimates of climate change impacts on snow (e.g. Son & Tague, 2018), vegetation growth (e.g. Vicente-Serrano et al., 2015), evapotranspiration (e.g. Tague & Peng, 2013), mortality (e.g. Tague et al., 2013), streamflow (e.g. Boisrame et al., 2019), urban development (e.g. Bell et al., 2019), vegetation type conversion (e.g. Bart et al., 2016), and land management (e.g. Khorchani et al., 2022).

Method and Infrastructure

In recent years we have made several key advances to RHESSys

  • RHESSys now includes a fully coupled fire spread and fire effects model. The fire spread model (Kennedy et al., 2017) based on WM Fire, models fire spread as a function of fuel moisture, windspeed, fuel volume and topography. The fire effects model simulates changes to vegetation as a function of fire spread parameters that approximate flame length and canopy structural parameters, including overstory and understory heights that are used to approximate the effects of ladder fuels (Bart et al., 2020). Example applications of RHESSYs-Fire include (Hanan et al., 2020; Kennedy et al., 2021).
  • RHESSys is an example of a spatially distributed hydrologic model where water and nutrients are routed between spatial units based on topography, surface, and subsurface drainage parameters. Routing in RHESSys has always included shallow subsurface and surface flowpaths between spatial units (patches) along with deeper groundwater (spatially aggregated to hillslope scales). This traditional topographically driven routing approach provides valuable insights into hillslope-to-watershed scale hydrologic processes – and their linkages with ecological processes. For example, this approach can be used to explore differential responses of upslope and riparian vegetation. What this approach misses however is finer scale lateral water transport that is often not driven by topographic gradients defined at coarse (10-100m patch) scales. Finer scale lateral water (and nutrient) transport is often driven by land cover heterogeneity. For example, the redistribution of water between open space and vegetated patches, or between roofs and lawns in the urban context. Explicit spatial modeling of these fine scale features and routing between them is rarely feasible for watershed scale models like RHESSys. However, an aspatial or implicit approach that accounts for heterogeneity and fine scale transfer within spatial patches is possible. We have now implemented a representation of within spatial patch heterogeneity and moisture/nutrient redistribution in RHESSys. This new aspatial approach is superimposed on the original spatially explicit routing within RHESSys. Application of this new approach allows the model to better account for forest density reduction (Burke et al., 2021; Tague & Moritz, 2019), species interactions (Rog et al., 2021) and urban eco-hydrology (forthcoming).
  • We have developed new tools to support RHESSys model set up, calibration, and output analysis in R (The R Project for Statistical Computing). These tools are distributed as a R-package called RHESSysIOinR and are available for download from GitHub (https://github.com/RHESSys/RHE...).
  • These tools utilize spatial analysis packages within R and allow RHESSys users to set up the model using spatial data as GeoTIFFs etc., and thus remove the need to install GRASS GIS (as was required by previous RHESSys set up). RHESSysIOinR also provides guidance on running parameter sensitivity analysis using R packages such as sensitivity (for Sobol-based sensitivity analysis) and LHR (Latin Hypercube). This package is still under development and we will be adding additional features.
  • A docker version of RHESSys is now available for download. This facilitates user applications across a wider variety of platforms. The docker version is available at https://hub.docker.com/r/lgrau...(also see workflows on RHESSys GitHub at https://github.com/RHESSys/RHE.../tree/trunk/.github/workflows" class="redactor-autoparser-object">https://github.com/RHESSys/RHE... & https://github.com/RHESSys/RHE.../blob/trunk/Dockerfile" class="redactor-autoparser-object">https://github.com/RHESSys/RHE...).

Additional Resources

RHESSys is open-source software and is under ongoing development. The code is maintained on GitHub and includes documentation and instructions for new users. The TagueTeamLab also offers occasional workshops and trainings for RHESSys users.

About the author: Naomi Tague is a Professor at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. She researches Ecohydrology and Ecoinformatics. More about Naomi and her research group can be found at TagueTeamLab.org.


Bart, R.R., Kennedy, M.C., Tague, C.L., McKenzie, D. (2020) Integrating fire effects on vegetation carbon cycling within an ecohydrologic model, Ecological Modelling 416: 108880. doi:10.1016/j.ecolmodel.2019.108880

Bart, R.R., Tague, C.L., Moritz, M.A. (2016) Effect of Tree-to-Shrub Type Conversion in Lower Montane Forests of the Sierra Nevada (USA) on Streamflow, PLoS ONE 11(8): e0161805. doi:10.1371/journal.pone.0161805

Bell, C.D., Tague, C.L., McMillan, S.K. (2019) Modeling runoff and nitrogen loads from a watershed at different levels of impervious surface coverage and connectivity to stormwater control measures, Water Resources Research 55(4): 2690-2707. doi: 10.1029/2018WR023006

Boisrame, G.F.S, Thompson, S.E., Tague C., Stephens, S.L. (2019) Restoring a Natural Fire Regime Alters the Water Balance of a Sierra Nevada Catchment, Water Resources Research 55(7): 5751-5769. doi.org/10.1029/2018WR024098

Burke, W.D., Tague, C., Kennedy, M.C., Moritz, M.A. (2021) Understanding how fuel treatments interact with climate and biophysical settings to affect fire, water and forest health: A process-based modeling approach, Frontiers for Global Change 3:591162. doi:10.3389/ffgc.2020.591162

Hanan, E.J., Ren, J., Tague, C.L., Kolden, C.A., Abatzoglou, J.T, Bart, R.R., Kennedy, M.C., Liu, M., Adam, J.C. (2020) How climate change and fire exclusion drive wildfire regimes at actionable scales, Environmental Research Letters 16(2): 024051. doi:10.1088/1748-9326/abd78e

Kennedy, M.C., Bart, R.R., Tague, C.L., Choate, J.S. (2021) Does hot and dry equal more wildfire? Contrasting short- and long-term climate effects on fire in the Sierra Nevada, CA., Ecosphere 12( 7):e03657. doi.org/10.1002/ecs2.3657

Kennedy, M.C., McKenzie, D., Tague, C., Dugger, A.L. (2017) Balancing uncertainty and complexity to incorporate fire spread in an eco-hydrological model, J. Wildland Fire 26(8): 706–718. doi:10.1071/WF16169

Khorchani, M., Nadal-Romero, E., Lasanta, T., Tague, C. (2022) Carbon sequestration and water yield tradeoffs following restoration of abandoned agricultural lands in Mediterranean mountains, Environmental Research 112203. doi.org/10.1016/j.envres.2021.112203

Rog, I., Tague, C., Jakoby, G., Megidish, S., Yaakobi, A., Wagner, Y., & Klein, T. (2021) Interspecific soil water partitioning as a driver of increased productivity in a diverse mixed Mediterranean forest, Journal of Geophysical Research: Biogeosciences 126: e2021JG006382. doi.org/10.1029/2021JG006382

Son, K., Tague, C. (2018) Hydrologic responses to climate warming for a snow-dominated watershed and a transient snow watershed in the California Sierra, Ecohydrology 12(1). doi:10.1002/eco.2053

Tague, C.L., Moritz, M.A. (2019) Plant Accessible Water Storage Capacity and Tree-Scale Root Interactions Determine How Forest Density Reductions Alter Forest Water Use and Productivity, Frontiers in Forests and Global Change 2:36. doi:10.3389/ffgc.2019.00036

Tague, C., Peng, H. (2013) The sensitivity of forest water use to the timing of precipitation and snowmelt recharge in the California Sierra: Implications for a warming climate, Journal of Geophysical Research: Biogeosciences 118(2): 875-887. doi:10.1002/jgrg.20073.

Tague, C.L., McDowell, N.G., Allen, C.D. (2013) An integrated model of environmental effects on growth, carbohydrate balance, and mortality of Pinus ponderosa forests in the Southern Rocky Mountains, PLoS ONE 8(11): e80286. doi:10.1371/journal.pone.0080286

Vicente-Serrano, S.M., Camarero J.J., Zabalza, J., SanGüesa-Barreda, G., López-Moreno, J.I., Tague, C. (2015) Evapotranspiration deficit controls net primary production and growth of silver fir: implications for Circum-Mediterranean forests under forecasted warmer and drier conditions, Agricultural and Forest Meteorology 206: 45-54. doi:10.1016/j.agrformet.2015.02.017