Countries around the world are experiencing record-breaking temperatures and the highest alert risk for wildfires. Many haven’t even recovered from months-long droughts. This is a big concern for places like the Netherlands, which has had little experience with prolonged dry and hot springs and summers. So what is at stake and what can we do about it? We asked our followers on social media what they wanted to know about heatwaves and droughts. Below is an overview compiled by our scientists that we will continue to update.

Heatwaves and droughts

Map of 2022 European heatwaves from 10 to 16 of July
Photo: Extreme maximum temperature (°C) for July 17 to 23, 2022 in Europe. Source: Wikimedia/NOAA

What qualifies as a heatwave, and what do we mean by drought?

Answered by Niko Wanders

A heatwave is a period of unusually high temperatures for more than two days. That ‘abnormality’ is determined in relation to the usual climate in a given area. In the Netherlands, for example, a heatwave is defined as at least five consecutive days with a maximum temperature of 25°C or above, including at least three ‘tropical’ days of temperatures above 30°C. Whereas in the plains of India, temperatures should reach at least 40°C to declare a heatwave.

While a heatwave is excessive heat, a drought is a shortage of water. A drought typically starts with a deficit of precipitation over an extended period of time, which leads to a reduction of soil moisture as well as shortages of water in streams, rivers, reservoirs and groundwater.

Heatwaves and droughts are closely related. The heat dries out soils, which further increases temperatures. Higher temperatures enhance the evaporation of surface waters such as rivers and lakes, reducing the quantity of an important source of freshwater for millions of people. During a heatwave, we also use more water for drinking, cooling or irrigating crops, which can further exacerbate water shortages due to droughts. And when heatwaves and droughts occur at the same time, like is the case in large parts of Europe this year, their impacts are even more brutal.

What is causing the droughts in the Netherlands? Is climate change the main cause?

Answered by Niko Wanders

Generally speaking droughts are always caused by a long period of below normal precipitation. In the Netherlands we see two major causes: one is not enough rain in the Netherlands; the other is not enough rain in the Alps and Germany, which results in reduced water levels in the Rhine river, which is the lifeblood of drinking water supply, agriculture, nature or shipping in the Netherlands.

When we studied the 2018 drought, we observed that droughts affect different areas of the Netherlands differently. In the lowlands, so west of Utrecht, and in the northern provinces, the leading cause of drought is a lack of rain in Germany and thus the lack of water in the rivers. In the south and east of the Netherlands, however, droughts are the result of increased evaporation due to warmer temperatures and local long dry periods.

This raised the question of whether droughts were caused by climate change. We concluded that global warming was responsible for the increased likelihood of droughts, at least in the Eastern part of the Netherlands, due to higher temperatures leading to increased evaporation. Coastal areas, however, experienced more summer rain and so far we cannot connect climate change to more droughts in the coastal region.

Apart from this complex interplay of factors, droughts can be further exacerbated by increasing human water demand, water losses from leaky old pipes or inefficiencies in water distribution and usage.

Can we expect these hot and dry years every year?

Answered by Niko Wanders

Our research shows that these kind of extremes are unfortunately becoming more frequent and more intense with a changing climate: in fact, years of extreme drought can occur almost three times more often.

If we look at the 15 driest years on record in the Netherlands since measurements started in 1901, five have taken place in the last decade alone (see figure 1 below). And 2022 is breaking new records. This year the Rhine flowed at historically low rates in April, and lower than ever observed in the month of August, bringing it close to the old time low from 1947 (see figure 2 below).


The 15 driest years on record in the Netherlands are 1921, 1925, 1934, 1947, 1949, 1952, 1964, 1976, 2003, 2006, 2015, 2018, 2019, 2020, 2022
Figure 1: Minimum discharge Rhine at Lobith in July. Source: Niko Wanders.

The reoccurrence of extremely dry years is particularly concerning because it makes following years more vulnerable to drought. Our analyses of the impact of three consecutive dry years (2018, 2019 and 2020) in the Netherlands and large parts of northern and western Europe show that soil moisture and groundwater levels didn’t recover fully in the winters in between.

That’s not surprising. The replenishment of groundwater levels following a drought takes time, months to years. Even when it starts to rain again, desiccated soils absorb less water. Rain from thunderstorms tend to wash away into sewers and rivers, rather than being retained by the soils. This way, the impacts of every hot and dry year are magnified by the existing dry conditions of previous years, which may result in longer than usual periods of drought, or even multi-year droughts.

Figure 2: Water discharge in the Rhine at Lobith (m3/s). Source: Niko Wanders (data Rijkswaterstaat)

What are the impacts of drought in the Netherlands?

Answered by Niko Wanders

The Netherlands is a water-rich country. But that abundance also makes it very dependable on water resources, so when there is a drought, the consequences are huge. From our analysis, the multi-year drought of 2018, 2019 and 2020 that struck large parts of northern and western Europe, including the Netherlands, has led to many problems even to this day, with some municipalities having to apply restrictions on water use.

Droughts hit the agricultural sector hard, reducing crop yields, grassland and farmers’ income. Low groundwater levels expose our flood risk infrastructure, debilitating the capacity of dikes to withstand the force of seawater. As groundwater declines, the land underneath our houses subside. It’s estimated that damages to houses due to land subsidence have cost Dutch taxpayers between 450 and 2080 million Euros (Ecorys 2018). In addition, low water levels in rivers have limited the load ships could carry, leading to higher costs for customers. Reduced quantity of surface waters such as lakes and rivers have impacted drinking water facilities and natural ecosystems. And as a result of lower water levels, saltwater infiltrates into our land, affecting the potability of freshwater resources, the fertility and productivity of farmland as well as nature.

How are these past dry years affecting the availability and quality of water in the Netherlands?

Answered by Michelle van Vliet

Recent droughts resulted in strong declines in streamflow of the Meuse and Rhine rivers, higher water temperatures and deterioration of water quality with respect to increased salinity levels, eutrophication issues, and higher concentrations of several pollutants (e.g. pharmaceuticals). When the river flow is low, there is less water available to dilute pollutants. This results in higher concentrations for several substances that may temporally exceed thresholds for drinking water, irrigation or other sectoral water use. For instance, higher water temperatures under droughts and heatwaves may result in constraints for power plants that use river water as main source for cooling. We have seen this for nuclear power plants in Belgium, Germany and Switzerland during the heatwave in mid-July 2022.

How does drought affect crops and food production? And what can we do about that?

Answered by Rashmi Sasidharan and Mariana Silva Artur

Plants need water for their growth and development, including the production of fruits, leaves, roots, and seeds that we humans consume. Plants obtain their water mostly from the ground. However, global warming has increased the occurrence of too much rain (flooding) or too little rain (drought) in different parts of the world. Both floods and droughts negatively affect plants. The severe drought that we are experiencing in Netherlands for example, means that plants cannot obtain sufficient water for their survival. For plant species that we grow for food, even if the plant itself survives, the limited water supply will severely reduce yield quality and quantity. This means less grain from cereal crops like rice and wheat and smaller or lesser number of carrots or potatoes. So drought directly impacts food production and increases costs.

At Utrecht University and Wageningen University & Research we investigate the effects of water stresses (drought and flooding) on plant survival to identify the mechanisms and genes that help plants cope in these unfavourable situations. With our findings we hope to contribute to the development of plants that are more tolerant to water stresses and to safeguard the future of food production in the Netherlands and in the world.

How does heat stress affect animals?

Animals cannot sweat as well as people can. Therefore it’s harder for them to get rid of excessive heat. On hot days, the result can be heat stress: the animal's temperature is abnormally high. If no action is taken at such times, animals may go into shock and organ damage may occur, with all the associated consequences. 

So what can be done? Prevention is the most important: make sure there is good ventilation, shade and plenty of water available for your animal. Never leave your pet in the car on a hot day. Not even in the shade with a window open. Take it easy during the hottest part of the day, so don't walk or romp with it at that time. Pay extra attention to animals that are old or have heart or respiratory problems. If your dog has been in the sun too long, it is important to cool down: make sure the animal is completely wet. No need for ice-cold water, tap water is fine. Don't wrap the animal in a wet cloth, because then it cannot lose its heat. And if you are worried: always contact your vet!

The Netherlands is renowned internationally for the fight against rising water levels. Are we prepared to deal with droughts?

Answered by Maarten Kleinhans

The fame of the Netherlands is only partly earned, because it is precisely the fight against water that made, and will make, problems worse in the future. The areas along the Rhine and Meuse rivers and the coastal areas have suffered a great many inundations in the past 900 years since the dikes and dams were built. These dikes and dams, and the water table lowering for cultivation, led to widespread subsidence and loss of peat. We have lost several meters of elevation over the past millennium. The land is already lowering as fast as the sea level will rise later this century, and the peat loss has contributed extra greenhouse gases.

The two past responses have been to lower the water table even further, and to try to get rid of flood water and precipitation as fast as possible. This means that the present water management system is not well suited for keeping water in the system. This makes the Netherlands more and more vulnerable to sea-level rise and to droughts.

Not only the Dutch but also the Germans, Belgians and French will discover that nature restoration is extremely powerful in keeping and infiltrating water. In the past, removal of forest, hedges and other forms of natural  landscape variability led to more infiltration and prevented fast accumulation of flow in streams and rivers that lead to downstream dike breaches and inundation. The catastrophic 2021 flood in the river Meuse was not only due to climate change but also due to a millennium of landscape change by urbanisation, eradication of ecosystems and large-scale agriculture. If the countries upstream of the Netherlands keep more of their water, that will reduce flood risk here. But they may also keep more water in summer, which reduces the river flow into the Netherlands and increases the drought problems.

The Netherlands may be internationally renowned for selling their expertise in short-term water management, but sustainable management will require radical changes in land use, nature rehabilitation, and a leading role in climate mitigation to prevent the worst.

How will our response to droughts affect the way we treat rising water levels during wintertime? And inversely, how our preparedness for rising seas may impact our capacity to deal with droughts?

Answered by Maarten Kleinhans

These links are complex. Much depends on how fast water levels rise during wintertime. A gradual rise of the rivers in winter means there is time for groundwater to spread from the channels, but sudden floods need to be guided safely out of the country as fast as possible. A gradual sea-level rise in this century means a greater difference in water level in and along the rivers, which may increase groundwater infiltration along the rivers. However, sea-level rise beyond, say, 2 meter, means that draconic measures are needed such as dike heightening and widening, or damming off the river mouth entirely and pump out the sea water. Moreover, higher water levels with lower river discharge in summer, and subsided polders, means that salty seawater penetrates further inland gradually. Drought in the polders already causes saline groundwater to surface, and flushing the salt out can only be done with fresh water.

So, there is no such thing as a free lunch. It is not a question of preparing for one and get the other one in the bargain. The Netherlands needs to prepare for double trouble and redesign water management and land use such that the worst effects of climate change are avoided. Moreover, these changes have to be at least neutral or better for climate mitigation and bending the killing biodiversity trend.

In the event of water shortages in the Netherlands, who has the highest priority to water?

Answered by Herman Kasper Gilissen

Under ‘normal’ conditions, in the Netherlands the water needs of virtually all types of use can mostly be met. Water can freely be extracted from the water system, although some types of use – in particular larger extractions of ground or surface water – are regulated through licensing or notification systems.

In case of (a threat of) water scarcity – a situation in which the (regional) water demand exceeds the available and accessible amount of water of a certain quality, the right to water of specific types of use can be further limited for the benefit of other types of use. This happens on the basis of a statutory priority of use, the so-called ‘verdringingsreeks’ (see Article 2.9 Water Act and Article 2.1 Water Decree). On the basis of this prioritization, flood protection and preventing irreversible damage to nature and landscapes (1) is given priority over 2) utility services (drinking water and energy production to guarantee the security of supply), 3) small-scale high-quality use (irrigation of capital-intensive crops and processing industrial process water), and 4) other types of use (shipping, agriculture, nature, industries, recreation, fisheries, and the production of drinking water and energy exceeding the security of supply).

In case of water scarcity, the lower-ranked types of use will first, temporarily, lose their right to water and/or can no longer claim public measures to provide water, and thus have to accept any loss. Water users can be confronted with explicit prohibitions to extract water from the water system. Public measures, both technical and administrative, can be taken to make the remaining water available on the location where and to whom it is needed.

All in all, water management authorities use the ‘verdringingsreeks’ to strategically and, in a given situation, determine which type of use should still be served and which measures should be taken in that respect.

Many other countries as well as the European Union have implemented a comparable prioritization system, although their categorizations and sequences of types of use may differ. In most cases, unlike in the Netherlands, the production of drinking water is considered of highest priority. This can be explained by the geographic location of the Netherlands.

Who should be responsible for storing water when it’s abundant? 

Answered by Herman Kasper Gilissen

The Dutch water system is designed in such a way that excess water is discharged to the sea as quickly as possible. This is mainly done to prevent the country from flooding. A downside of this approach is that the availability of fresh water can become limited in times of drought and/or decreased river inflow, increasing the risk of water scarcity.

One of the potential strategies to decrease the risk and effects of water scarcity is to better hold and store excess water instead of discharging it (‘vasthouden en bergen’). Yet, there is no very clear division of responsibilities for storing water. Water storage can take place, on a (very) large scale, in the water system, for example by increasing water levels of surface water bodies such as the IJsselmeer, by giving water courses more room to meander or expand, or by creating water storage areas. Since such measures are to be taken within and become part of the water system, it is obvious that the responsibility thereto primarily lies with the Dutch water management authorities at the central and regional levels.

However, taking such measures requires a lot of room and can easily conflict with other spatial claims (housing, agriculture, nature). Therefore, this public responsibility should not be seen as absolute and exclusive; there is no responsibility for the government to guarantee the provision of water of a proper quality to all types of use at all times and all places.

Water (rain water or water extracted from the water system) can also be stored on a smaller scale, outside of the water system, such as in ponds, basins, and barrels. This is generally considered an individual responsibility of private parties (residents, farmers) and can effectively increase their resilience against droughts. Although not explicitly required by law, this responsibility could be derived from the obligation for individuals and companies to actively prevent and/or limit any damages where reasonably possible.

So to answer the question: although water system management certainly entails a responsibility for the government to take measures to decrease the risk of water scarcity, this does not mean that there is no (additional) responsibility for private parties to provide for their own (emergency) water supply.      

Are there efficient and sustainable ways to obtain drinking water from saltwater?

Answered by Edward Jones

Desalination – the process of removing the salts contained within saline water – has long been used to supplement water resources contained in rivers, lakes and groundwater. While historically concentrated in highly water scarce world regions, technological advances combined with increasing pressure on available water resources is increasingly making desalination an attractive and cost-competitive water resource management option worldwide. The proposition of securing a virtually unlimited, drought-proof and reliable supply of high quality water makes seawater desalination particularly attractive.

Yet, despite rapid technological advances, challenges related to the high economic costs, large energy requirements (often met by fossil fuels) and disposal of effluent associated with desalination remain persistent. While the use of renewable sources of energy for desalination is on the increase, the direct use of these energy sources is still in its relative infancy (less than 1% of global desalination capacity). Small projects show promise but can be difficult to scale. Of course, decarbonisation of electricity grids that supply desalination plants is also important for lowering greenhouse gas emissions.

While desalination has enormous potential, countries should also place a strong emphasis on maximising the use of water that is already available to us. This includes increasing water conservation efforts and improving water use efficiencies, but also through re-using our treated wastewater. Many countries already produce and release substantial volumes of treated wastewater to the environment, when instead direct re-use could be a feasible option to reduce the strain on other freshwater resources.

Which plants and trees can help get more rain? 

Answered by Rashmi Sasidharan and Mariana Silva Artur

It is not fully understood how plants influence the water cycle. However, forests do have a positive influence on rainfall patterns. The water that is pulled up by plant roots, is ultimately released (evaporated) into the environment. If we think of big forest trees, the amount of moisture this evapotranspiration process could release into the environment can be so much that it contributes towards increased rainfall. Thus, forests can boost rainfall. This evapotranspiration effect of plants also lowers the surrounding temperatures leading to a cooling effect. Thus more trees and plants in gardens and urban areas can bring much needed relief during heatwaves in addition to providing shade. Another contribution of plants to the water cycle is through their root systems. Plant roots hold the soil together preventing erosion during rainfall, and also assist in better water infiltration.

Meet our experts

  • Niko Wanders

    Assistant Professor Hydrological Extremes at Utrecht University
  • Dr. Michelle van Vliet

    Michelle van Vliet

    Associate Professor at the Department of Physical Geography of Utrecht University
  • Rashmi Sasidharan

    Rashmi Sasidharan

    Associate Professor of Plant-Environment Signaling at Utrecht University
  • Maarten Kleinhans

    Professor of river and delta biogeomorphology at Utrecht University
  • Dr Herman Kasper Gilissen

    Herman Kasper Gilissen

    Associate Professor of Administrative and Environmental Law for the Institute for Jurisprudence and Constitutional & Administrative Law/Utrecht Centre for Water, Oceans and Sustainability Law of Utrecht University
  • Edward Jones

    PhD candidate in the Department of Physical Geography at Utrecht University

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