Drought Modeling to Support Water Planning and Management

There has been a great deal of discussion about flood modeling for years now, and tools for simulating flood events—along with their output in the form of flood hazard maps—are widely available —both for open watercourses, coastal areas, and cities—covering flash floods and urban flooding associated with waterlogging in areas without drainage or due to inadequate storm drains. Hydraulic “flood” models are used to assess the effectiveness and efficiency of measures, both in planning documents (such as flood risk management plans) and in concepts or feasibility studies for planned measures and investments.

A drought is a phenomenon characterized by a prolonged water deficit in the environment, most often caused by below-normal precipitation, combined with the effects of factors such as evaporation, soil conditions, land use, and surface and groundwater resources. This is one of many definitions, focusing on hydrological issues. However, we know that this is not enough to effectively manage this phenomenon or plan measures to minimize its effects.

Drought is not a uniform hydrological phenomenon, but rather a process that develops over time and affects successive components of the water system and the environment. It may begin with a shortage of precipitation, then lead to a decrease in soil moisture, reduced water availability for plants, lower streamflow, and a drop in groundwater levels. Therefore, assessing drought requires an approach that integrates meteorological, hydrological, and hydrogeological aspects—and, consequently, agricultural considerations.

Is it possible to model the phenomenon of drought?

This raises the question of whether, given the wide range of aspects of drought, it is possible to model them. Of course it is. Moreover, today it is one of the tools used to support the planning of adaptation measures. However, it is important to remember that there is no single universal tool that describes all aspects of drought in exactly the same way, since meteorological, agricultural, hydrological, and hydrogeological droughts affect different components of the environmental system. The tool is therefore selected based on the elements being subjected to detailed analysis.

Climate models, meteorological models, and precipitation indices—such as SPI, SPEI, and the precipitation–evapotranspiration balance—are used to model meteorological drought. Agricultural (soil) drought is analyzed using soil water balance and evapotranspiration models, such as FAO-56, SWAT, and AquaCrop. Hydrological drought analyses employ precipitation–runoff models and watershed models, such as SWAT, HEC-HMS, MIKE SHE, and HBV; while hydrogeological drought is analyzed using groundwater flow models, such as MODFLOW, or integrated models like MIKE SHE.

Integrated Modeling of Water Processes

As has already been emphasized, drought is not a single, simple phenomenon, but rather the result of the interaction of many processes: insufficient precipitation, increased evaporation, limited infiltration, changes in runoff, a decline in soil moisture, and a drop in groundwater levels. This is precisely why analyzing drought requires tools that allow us to view the entire water cycle in an integrated manner, rather than focusing on just one specific element of the system.

Drought modeling not only makes it possible to describe where and when water shortages may occur, but also to understand why they occur and what measures can mitigate their effects. This makes it possible to compare scenarios involving climate change, land use, or the implementation of water retention measures, and to assess their impact on water resources at the local and watershed levels.

There are several tools available on the market that allow for comprehensive hydrological and hydrogeological analyses, such as SWAT and MODFLOW, but MIKE SHE, from the MIKE family, is one of the most advanced and comprehensive tools and best integrates the processes occurring at the watershed scale.

MIKE SHE allows for the simultaneous modeling of processes occurring on the land surface, in the soil, in the unsaturated zone, in groundwater, and in surface watercourses. It is precisely this integrated perspective that makes drought modeling not only possible but also useful in design, planning, and decision-making.

MIKE SHE – The Beginning

The name MIKE SHE is derived from an earlier project, the Système Hydrologique Européen (SHE), or European Hydrological System. The model, which has been developed since the late 1970s by European institutions, was incorporated into the MIKE family of tools developed by DHI, hence its current name. MIKE SHE’s long history of development is a significant advantage, as it attests to the maturity of the modeling concept, a solid methodological foundation, and many years of refinement in response to the needs of hydrological practice and research.

MIKE SHE – Technical Specifications

MIKE SHE is an advanced hydrological modeling tool that enables comprehensive simulation of the processes occurring in the hydrological cycle. This system allows for a detailed analysis of water flow both on the surface and underground, integrating processes such as infiltration, evaporation, surface runoff, and groundwater flow. Thanks to its modular design, MIKE SHE can be tailored to the specific needs of a project, taking into account a variety of environmental and management conditions.

A key feature of MIKE SHE is its flexibility in choosing how to describe processes. Depending on the purpose of the analysis and the availability of data, the model can use both fully physics-based approaches, which describe processes using flow equations, and simplified conceptual methods. This makes it possible to adjust the level of detail in the model—from general analyses at the watershed scale to more advanced simulations requiring an accurate representation of processes in the environment.

However, it is important to remember that the model in MIKE SHE, like any model, is a simplification of the real-world system; its results are subject to uncertainty, and their accuracy depends on the quality and accuracy of the data used.

The scope of the data and processes included in the hydrological model built in MIKE SHE is outlined in the diagram below:

MIKE SHE – The Practical Aspect

In practice, MIKE SHE is widely used in the analysis of water retention measures, such as the construction of water reservoirs, the implementation of small-scale retention systems, and the restoration of wetlands. It enables the assessment of the effectiveness of these solutions in reducing stormwater runoff, increasing water resources, and reducing flood risk. Below is a list of analyses that can be performed using the MIKE SHE model in the area of drought management and mitigation:

• Analysis of a watershed’s water balance—this helps answer the following questions: how much water enters the system from precipitation, how much is lost through evapotranspiration, how much infiltrates into the ground, and how much runs off over the surface and through the ground.
• Analysis of soil moisture and soil drought—enables the assessment of: changes in soil moisture over time, the duration of water deficits in the root zone, and the spatial variation of agricultural drought.
• Groundwater recharge analysis—allows for an assessment of: where and to what extent effective infiltration occurs, how recharge into aquifers varies, and how long the effects of dry spells persist.
• Simulation of changes in groundwater levels—the following can be analyzed: the decline in the groundwater table during prolonged droughts, the rate at which groundwater reserves recover after wet periods, and the impact of retention or infiltration measures on groundwater levels.
• Analysis of low flows and base flows— enables the assessment of: the impact of drought on stream flows, the reduction in base flow supplied by groundwater, and the timing and extent of the decline in surface water resources.
• Assessment of the impact of retention measures on mitigating the effects of drought—it is possible to compare scenarios involving measures such as: small-scale retention, wetland restoration, increased soil retention, renaturation of watercourses and valleys, and measures to slow runoff; the model shows whether a given measure: increases infiltration, improves soil moisture, raises the groundwater level, or stabilizes flows during dry periods.
• Assessment of the impacts of land-use changes —it is possible to analyze the effects of: urbanization, soil sealing, afforestation, changes in agricultural practices, and wetland conversions; This is very important in the context of drought, because land use affects: infiltration, runoff, evaporation, and landscape retention.
• Analysis of climate scenarios —can be used to assess the impacts of: a decrease in total precipitation, changes in the seasonality of precipitation, longer dry spells, and increases in temperature and evapotranspiration.
• Identification of areas particularly vulnerable to drought —based on the model’s results, the following can be identified: areas with low water retention, areas with rapid runoff, regions prone to falling groundwater levels, sections of watercourses particularly at risk of low-water conditions, and habitats dependent on shallow groundwater.

The following is a summary of the specific features of the MIKE SHE tool, along with an example of its application and the benefits it offers for a given project or decision.

The MIKE SHE Feature	Example Application	Benefit to the project/decision
Modeling Precipitation, Infiltration, and Surface Runoff	Assessment of the Impact of Retention Measures in a Watershed	A better understanding of where and to what extent rapid runoff can be reduced and retention increased
Flow Simulation in the Unsaturated Zone and in Groundwater	Analysis of Aquifer Recharge and the Effects of Artificial Infiltration	The ability to assess changes in groundwater levels and the impact of activities on water resources
Integration of surface and underground processes	Assessment of the Relationships Between Wetlands, Watercourses, and Groundwater	A more comprehensive picture of how the watershed functions and a better basis for planning adaptation measures
Analysis of Land Use Scenarios	Comparison of the current option with urbanization, renaturalization, or reforestation	Support for selecting the option with the most favorable water balance and the lowest hydrological risk
Assessment of Adaptation Options	A Comparison of Solutions for Drought, Floods, and Climate Change	The ability to identify the most technically and environmentally effective measures
Spatial presentation of results	Maps of infiltration, outflow, groundwater recharge, and retention areas	A clear presentation of the results to stakeholders and an easier way to justify recommendations

Examples of use and testimonials from Poland and around the world

The hydrological models developed in MIKE SHE have served as the basis for numerous analytical studies and systems in Poland and around the world. Practical applications of MIKE SHE include both analyses of water resources and environmental impacts, as well as the design of adaptation measures to address drought and improve water retention. The model has been used, among other places, in the Mokolo River watershed in South Africa to simulate hydrological scenarios for the management of environmental flows, in the Aa of Weerijs watershed to evaluate nature-based solutions (NBS) that mitigate the effects of drought, as well as in research on the links between climate and hydrology in the Skjern River watershed in Denmark.

A key feature of the MIKE SHE tool is its dynamic integration with the surface water model—previously developed in MIKE11 and now in MIKE+. Examples include the globally unique water resources management system for the Murrumbidgee River basin (an 85,000^km² basin), CARM—Computer Aided River Management—which received the prestigious Australian Environmental Engineering Excellence Award in 2013. Another example is the Big Cypress Basin Real-Time Hydrologic Monitoring and Modeling System implemented by the South Florida Water Management District (SFWM), which manages water resources in the extremely sensitive and ecologically valuable areas of South Florida (including areas of the Everglades National Park and Lake Okeechobee, with a surface area of 1,891^km²). The SFWM also used the MIKE SHE and MIKE 11 models to simulate the Alligator Lake watershed, the Caloosahatchee River watershed, the Everglades National Park nutrient removal system: Everglades Nutrient Removal, the 930^km² Estero Bay watershed—which contains 37 lakes and 15 rivers—and the 7,770^km² Kissimiee River watershed.

In recent years, MIKE SHE has also been used in the German project “Wassermanagement unter Berücksichtigung des Klimawandels.” The project’s goal is to prevent the excessive use of available water resources and conflicts over their use. All key stakeholders responsible for water management or who use water within the project area have been involved in the project. To achieve this goal, an integrated model was developed in collaboration with all stakeholders to serve as a tool for forecasting and decision support. It will serve as the basis for planning and implementing specific measures, combinations of measures, and adaptation strategies within the project area. More details and materials can be found on the project website: https://wlv.de/landwirtschaft-klimawandel.

In Poland, MIKE SHE was used, among other things, to carry out the project “Hydrogeological Documentation Determining the Available Groundwater Resources of the Gostyń Watershed ” and to forecast hydrogeological conditions and groundwater salinity in the coastal zone of Gdańsk Bay under the influence of the projected rise in due to climate change (Polańska K., 2009, doctoral dissertation at the University of Gdańsk, Faculty of Oceanography and Geography). In the area of retention issues—and thus also those aimed at minimizing the effects of drought—MIKE SHE models were used to analyze the potential for increasing retention in forested, agricultural, and urbanized areas within the Wkra and Pilica river basins as part of efforts to maintain and increase existing retention capacity in the Middle Vistula Water Region. The project results are available at: http://www.retencjawisla.pl/. The Regional Water Management Authority in Warsaw conducted these analyses as part of its initial flood risk management plans.

Resources and Training

There are many free resources available online that can help you learn more about the MIKE SHE tool, get started, or improve your skills in hydrological modeling.

• Introductory Course on Modeling in MIKE SHE
  👉 The course is available at this link: Getting Started with MIKE SHE
• Monthly webinars showcasing the features of the MIKE SHE tool
  👉 List of upcoming sessions: Upcoming MIKE SHE Webinars
• Recordings of previous webinars featuring MIKE SHE – available upon request

👉 Introductory webinar on building a model in MIKE SHE: How to Build a Model in MIKE SHE – Part I

👉 Introductory webinar on MIKE SHE model calibration: How to Build a Model in MIKE SHE – Part II

👉 Introductory webinar on postprocessing data from the MIKE SHE model: How to Build a Model in MIKE SHE – Part III

• A step-by-step guide with specific analyses in the MIKE SHE tool

👉 The guide is available at the following link: manuals.mikepoweredbydhi.help/latest/Water_Resources/MIKE SHE Exercises.pdf

• MIKE SHE User Manual and Technical Documentation

👉Documentation available at the following link: MIKE SHE Documentation

Why don’t we use such tools in strategic planning?

It seems that developing a reliable model would help answer many questions raised by water managers and water users. So why aren’t we using it? The most common reason is quite simple: the tools exist, but the planning system is not yet fully ready to use them on a routine basis. There are quite a few problems and difficulties.

Integrated models require large amounts of high-quality data: meteorological, hydrological, hydrogeological, and soil data, as well as information on land use and water and drainage infrastructure. In Poland, this data is often scattered across various institutions, inconsistent, of varying resolution, difficult to obtain, and not always up-to-date or complete. Without it, even a very good model cannot produce results that are sufficiently reliable for planning purposes.

Another problem is the high complexity of the models: they are time-consuming to build, require calibration and validation, and need an experienced team. In urban planning practice, people often look for faster, simpler, and cheaper methods. Developing such models involves fairly high costs—both for their creation and for keeping them up to date if they are to be used in the long term.

Furthermore, there are no planning procedures that require the use of integrated models. Typically, the focus is on meeting minimum methodological requirements, and indicators, expert analyses, and simpler assessments are preferred. An integrated model, as the name suggests, combines various fields, and this is where we encounter another problem—the division of institutional responsibilities. Drought simultaneously affects water management, agriculture, land-use planning, environmental protection, forestry, and infrastructure. This results in fragmented responsibility, whereas integrated models require precisely the integration of data, objectives, and decisions across sectors. Unfortunately, even a good model is not enough if there is no clear mechanism for implementing the results; the results do not translate directly into policy provisions; and decision-makers expect simple recommendations, while the model reveals complex interdependencies and uncertainty.

Summary

The use of modeling tools in drought analysis is crucial because it allows us to move from a general diagnosis of the problem to a quantitative assessment of the processes responsible for water deficits and the effectiveness of possible mitigation measures. Modeling makes it possible to simultaneously account for the influence of meteorological conditions, soil properties, land use, surface runoff, groundwater recharge, and the relationships between watercourses and aquifers.

In this context, MIKE SHE stands out as a particularly useful tool, as it enables an integrated analysis of the entire water cycle within a watershed and, thus, an assessment of various forms of drought—from soil drought, through hydrological drought, to hydrogeological drought. Its particular value lies in its ability to analyze climate change scenarios, land-use changes, and various adaptation and retention measures, making it not only an analytical tool but also a practical aid for planning, decision-making, and building long-term resilience to drought.

Despite the availability of advanced modeling tools, their use in drought planning in Poland remains limited. This is primarily due to stringent data requirements, the fragmentation of information across institutions, the high complexity and costs of model development, and the lack of a formal obligation to use such tools in many planning procedures. The sectoral division of responsibilities certainly does not facilitate the process. Another significant challenge remains translating complex modeling results into simple, actionable recommendations that can be incorporated into strategic and planning documents.

A drought is definitely harder to “visualize” than a flood. It’s not enough to simply show the extent of flooding on a map. It’s also harder to mitigate. Drought develops more slowly and in multiple dimensions—precipitation, soil moisture, runoff, and groundwater levels all play a role, and its effects impact many sectors. This makes it harder to create a single, simple, and universally understood planning tool. However, the droughts that have struck Poland and most of Europe in recent years—and continue to do so annually—seem to be a good motivator for launching in-depth analyses in this area. This issue should encourage greater awareness when issuing decisions or permits regarding water withdrawals and discharges, better planning of adaptation measures, and cross-sectoral cooperation. If implementing this at the national level is not feasible in the short term, it may be worth starting with the regions most severely affected by drought. Tools such as MIKE SHE and others are available, and the difficulty of using them should not be a mere excuse for ignoring this opportunity or for making less informed decisions regarding water planning and management in light of drought.

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Source: DHI material