Spatial Analysis of Evapotranspiration(ET) and Precipitation(P) in Germany (2013-2022): A Study on Water Balance and Budget

-Aysha Akter,
Student of AGSRT

INTRODUCTION

Water balance, a fundamental concept in hydrology, represents the equilibrium between water inputs and outputs within a given area over a specific period. This balance is crucial for understanding the sustainability of water resources, managing agricultural practices, and mitigating the impacts of climate change. Two primary components of water balance are evapotranspiration (ET) and precipitation (P).

Evapotranspiration is the process by which water is transferred from land to the atmosphere by evaporation and transpiration. In simpler terms, it's the amount of water transpired by plants and evaporated from the ground/soil and surface water. It is a significant factor in the hydrological cycle, influencing soil moisture, groundwater recharge, and river flow. Precipitation, on the other hand, is the primary source of water input into the hydrological cycle. The interplay between ET and P determines the availability of water for various ecological and human activities.

Germany, located in Central Europe, experiences a temperate climate with moderate to high precipitation and well-distributed seasonal variations. Understanding the spatial distribution and temporal trends of ET and P in Germany is essential for effective water resource management, particularly in the context of climate change, which can alter precipitation patterns and evapotranspiration rates.

Objective:

The main objective of this project is to conduct a spatial analysis of evapotranspiration and precipitation to study the water balance in Germany from 2013 to 2022. By examining the spatial distribution and trends of ET and P over this decade, we aim to identify regions with water deficits or surpluses and understand the underlying factors contributing to these patterns.

Relevance:

This study holds significant relevance for several reasons. Firstly, it provides insights into the hydrological dynamics of Germany, a country with diverse climatic and geographic conditions. Secondly, understanding the spatial and temporal variations in ET and P can aid in predicting the

impacts of climate change on water resources. Thirdly, the findings of this study can inform water management policies and strategies, ensuring the sustainable use of water resources in Germany.

Water balance analysis is particularly important in the context of climate change, which is expected to increase the frequency and intensity of extreme weather events, such as droughts and floods. By analyzing data from the past decade, this study can contribute to the development of adaptive measures to mitigate the adverse effects of these events.

This project aims to provide a comprehensive understanding of the spatial distribution and temporal trends of evapotranspiration and precipitation in Germany from 2013 to 2022. Through detailed spatial analysis, this study will offer valuable insights into the water balance of the region, supporting effective water resource management and policy-making.

Study area:

Germany is strategically located in the heart of Europe, is bordered by nine countries: Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, and France, Luxembourg, Belgium, and the Netherlands to the west. This central location is making it a central hub for both political and economic activities on the continent. Its geographical coordinates range from approximately 47°16'N to 55°03'N latitude and 5°52'E to 15°03'E longitude. The country's total area is approximately 357,022 square kilometers, making it the seventh-largest country in Europe.

Germany's diverse climatic and geographic conditions make it an ideal study area for analyzing water balance. The interplay between evapotranspiration and precipitation varies across different regions, influenced by factors such as topography, climate, vegetation, and land use, affects water availability, distribution, and management. By examining these variations over the decade, this study aims to provide valuable insights into the hydrological dynamics of Germany. Such insights can inform water resource management policies, helping to mitigate the impacts of climate change and ensure the sustainable use of water resources.

[Map 1: Geographical location of the Study Area]

Literature review :

The spatial and temporal analysis of evapotranspiration (ET) and precipitation (P) plays a critical role in understanding the water balance and its implications for various environmental and hydrological processes. Numerous studies have been conducted to investigate the dynamics of ET and P, particularly in the context of climate change, water resource management, and ecological sustainability. This section reviews key literature that forms the foundation of the current study, focusing on the methodologies and findings relevant to Germany.

Evapotranspiration is a vital component of the hydrological cycle, encompassing the combined processes of evaporation and transpiration. Jung et al. (2010) utilized satellite-based remote sensing data to analyze global patterns of ET, emphasizing the significance of accurate ET measurements in understanding regional water cycles. Their findings highlighted the variability of ET across different climatic zones and underscored the need for high-resolution data in hydrological studies.

In the context of climate change, Mueller et al. (2011) examined trends and variability in global ET by integrating in situ observations with model simulations. Their research demonstrated that climatic factors such as temperature and precipitation significantly influence ET trends, with potential implications for water resource management. Similarly, Fischer et al. (2013) projected changes in ET patterns in Europe due to rising temperatures and altered precipitation regimes, stressing the importance of adaptive management strategies in mitigating adverse impacts.

Precipitation is another critical element of the water balance, directly affecting water availability and ecosystem health. Zolina et al. (2008) conducted a comprehensive analysis of long-term trends and variability in European precipitation, utilizing high-resolution datasets. They identified significant regional differences in precipitation patterns, influenced by large-scale atmospheric circulation. This study provided valuable insights into the temporal dynamics of precipitation, which are essential for regional water balance assessments.

Further, Maraun et al. (2010) explored the impact of climate change on extreme precipitation events in Europe, finding an increase in both the frequency and intensity of such events. This research highlighted the potential for heightened flood risks and the need for robust flood management practices. Blöschl et al. (2019) reviewed recent changes in European hydrology, including precipitation trends, and discussed their implications for water resources, emphasizing the importance of integrating hydrological and climatic data for comprehensive water balance studies.
The interplay between ET and P is crucial for understanding the water balance at various spatial and temporal scales. Samaniego et al. (2010) integrated ET and P data to model the water balance in Germany using a high-resolution hydrological model. Their study highlighted the importance of spatially and temporally resolved data for accurate water balance assessments and provided a framework for analyzing regional water dynamics.
Trenberth et al. (2014) provided a global perspective on the water cycle, emphasizing the interconnections between ET, P, and other hydrological components. Their research stressed the need for integrated approaches to understand regional water balances in the context of global climate change. Huntington (2006) reviewed the implications of climate change on the global water cycle, focusing on the interactions between ET and P. The study discussed potential changes in water availability and the importance of adaptive management strategies to address emerging challenges.

Data and Methods:

[Fig 1: Model of Steps]

1.Steps to analysis the Mean of ET and P:

The First step for analysis of the Mean of Evapotranspiration (ET) and Precipitation (P) was, Loading ET and P Monthly raster data and Germany boundary shapefile into ArcGIS Pro. Then to ensure all datasets are in the same coordinate system, use a reprojected coordinate system. After that, applied “Composite Raster'' tools to composite all the Bands, like for the year 2013, composited first 12 Bands (from 1 to 12 Bands), for the year 2022, composited last 12 Bands (from 109 to 120 Bands), and for the year from 2013 to 2022, composited all the 120 Bands (from 1 to 120 Bands). Next, utilized “Cell Statistic” tools to compute the sum and mean of ET and P. Then for calculating the Mean of ET and P, I used “Raster Calculator” tools (to compute the mean of ET and P only from 2013 to 2022). Then I utilized “Raster to Point '' tools to convert the Raster data to point feature. Next, I utilize the “IDW '' tool to interpolate ET and P values for the year 2013, 2022 and from 2013 to 2022. Following that, to clip the ET and P data to the Germany boundary, I Used the 'Extract by Mask' tools. Next, I applied an appropriate color ramp to visualize the average ET, P and Annual Average of ET and P later. Last but not the least, I created a new Layout and added the Map View and also inserted Title, Legend, North arrow, and a Scale bar to Export the Map. For Calculation the Water Balance I Used Python.

Results and Discussions:

1.Evapotranspiration in the year 2013:

[Map 2: Evapotranspiration in 2013]

The Map 2 illustrates the spatial distribution of evapotranspiration rates across Germany for the year 2013, showing significant regional variations influenced by vegetation cover, land use, and climatic conditions as well. Lower ET rates are more prevalent in Eastern and Northern Germany, shown by the light blue and teal areas. - These regions may have less dense vegetation, lower precipitation levels and low water availability, contributing to lower ET rates. On the other hand, Western and Southern regions generally show higher ET rates, indicated by the green, red, and dark red areas, often corresponding to densely forested or highly vegetated areas with significant rainfall. In Central Germany - a mix of ET rates can be observed. The green areas indicate moderate ET rates. Possible Reasons might be agricultural lands, mixed landscapes, or areas with moderate vegetation and precipitation. - The map provides a visual representation of ET rates across Germany for the year 2013. Variations in ET are influenced by factors such as vegetation cover, land use, and climatic conditions. Understanding these patterns is essential for effective water management, agricultural planning, and environmental conservation.

2.Evapotranspiration in the year 2022:

[Map 3: Evapotranspiration in 2022]

The above Map 3 depicts the distribution of evapotranspiration (ET) rates across Germany in 2022. Western and Southern regions exhibit higher ET rates, shown in green, purple, and red. High ET rates in regions such as the Black Forest and parts of Bavaria are due to dense forests and increased precipitation. Moderate ET rates/zones (green), found in central Germany and some parts of the north and south, often related to agricultural lands or mixed-use areas, reflecting diverse land use and vegetation. Eastern and Northern regions; - These regions display lower ET rates, indicated by light blue and teal. - Likely due to sparse vegetation and lower rainfall. The map illustrates the varying evapotranspiration rates across Germany for 2022, highlighting how different regions are affected by factors. Understanding ET rates aids in the efficient management of water resources, essential for both urban planning and agricultural activities, crucial for climate models and understanding the impacts of climate change on water cycles.

3.Precipitation in the year 2013:

[Map 4: Precipitation in 2013]

The map 4 presented up illustrates the spatial distribution of precipitation across Germany for the year 2013. The data has been classified into five distinct precipitation ranges, each represented by a different color for clarity and ease of interpretation. The highest levels of precipitation, ranging from 5.3 to 9.8 mm, are shown in red. These areas are predominantly located in the southernmost part of Germany, particularly in the mountainous regions, which are known for receiving higher levels of precipitation. The green and purple regions show areas where precipitation levels were moderate, ranging from 2.2 to 5.2 mm. This category covers a substantial portion of the country, particularly in the northeastern and southwestern regions as well as these regions are more localized and can be found also scattered throughout Germany, particularly in the central and southeastern parts. By contrast, the areas depicted in blue and light cyan represent regions with the lowest annual precipitation, ranging from 0.7 to 2.1 mm. These regions are predominantly located in central and north-central Germany, some parts of the northwest as well as are more dispersed across the country but are notably present in the northern and southern parts of Germany.

The spatial distribution of precipitation in 2013 reveals significant regional variability. The central and northern parts of Germany generally experienced lower precipitation levels, while higher precipitation levels were observed in the southern regions, particularly in the Alps. This distribution is consistent with the geographical and topographical influences on precipitation patterns, where mountainous areas tend to receive more precipitation due to orographic lift. Understanding these patterns is crucial for water resource management, agricultural planning, and preparing for hydrological extremes such as floods or droughts.

3.Precipitation in the year 2022:

[Map 5: Precipitation in 2022]

The map 5 above depicts the spatial distribution of precipitation across Germany for the year 2022. The data is categorized into five distinct classes of precipitation, each represented by a different color to enhance visual interpretation. The regions depicted in shades of blue (0.6 - 1.1 mm) and light cyan (1.2 - 1.4 mm) represent areas with low annual precipitation. These areas are primarily located in the northern and northeastern parts of Germany, indicating relatively dry conditions. The low precipitation in these regions could be due to various climatic factors, such as lower frequency of rainfall events or the influence of continental air masses.

The green areas on the map represent regions with moderate precipitation, ranging from 1.5 to 2.1 mm. These regions are distributed across the central parts of Germany, extending into some northern and western areas. The moderate precipitation levels in these regions suggest a balance between dry and wet conditions, which is typically conducive to agricultural activities and maintaining ecological balance. The regions shown in purple (2.2 - 3.3 mm) and red (3.4 - 5.5 mm) indicate areas with high annual precipitation.

The spatial distribution of precipitation in 2022 reveals significant regional variability across Germany. The northern and northeastern regions generally experienced lower precipitation levels, while the central and southern regions received higher amounts of rainfall. This distribution is crucial for understanding regional water resource availability, agricultural productivity, and potential hydrological hazards such as droughts or floods. The map highlights the need for region-specific water management strategies to address the diverse climatic conditions across the country.

Annual Average Map of P from 2013 to 2022:

c)

[Map 7: a) P in 2013, b) P in 2022, and c) Annual Average P between 2013 and 2022]

This Map 7 contains three maps indicating the spatial distribution of precipitation in Germany for different time periods. Map (a) and (b) show the spatial distribution of precipitation across Germany for the year 2013 and 2022 respectively. Whereas Map (c) depicts the annual average precipitation over the period from 2013 to 2022. This map aggregates the precipitation data over a decade, showing the long-term trends and cumulative precipitation across Germany.
By examining maps, a) and b), which represent the precipitation in Germany for the years 2013 and 2022 respectively, we can observe significant changes in precipitation patterns over the decade. In 2013, high precipitation zones (5.3 - 9.6mm) were more prominent, particularly in Southern Germany. Whereas In 2022, the highest precipitation zones have reduced to 3.4 - 5.5mm, indicating a general decrease in maximum precipitation levels. In 2013, areas with very low precipitation (0.7 - 1.6mm) were less widespread. while, the spread of very low precipitation zones (0.0 - 1.4mm) has increased in 2022, particularly in the northern and central parts of Germany.

This map highlights long-term precipitation trends, helping to identify areas prone to drought or flooding. Areas with high cumulative precipitation may face challenges related to waterlogging and floods, while low precipitation regions might experience droughts and water scarcity. The average precipitation map (2013-2022) underscores regions with stable precipitation patterns, essential for understanding long-term climatic trends and water resource management. These maps are crucial for hydrological studies, climate modeling, and agricultural planning, providing valuable data on precipitation dynamics in Germany.

Water Balance/Budget Analysis:

[Fig 2: a) Annual and b) Monthly Average ET and P and Water Budget in Germany (2013- 2022)]

Water Balance/Budget Calculation:

Water Balance / Budget = Precipitation (P) – Evapotranspiration (ET)

The provided figure 2(a) depicts the trends in annual average evapotranspiration (ET) and precipitation (P) in Germany over the period from 2013 to 2022, along with the resulting water budget (P - ET). The annual average evapotranspiration and precipitation remains relatively stable throughout the decade, fluctuating around 12 mm/year and 2 mm/year respectively. Minor variations are observed, with slight increases or decreases from year to year, but overall, the trend is relatively consistent.

The water budget values are consistently negative, ranging between -9.0 and -10.0 mm/year. There are fluctuations within this range, with noticeable peaks and troughs indicating annual variations. The water budget appears to be lowest around 2016 and highest around 2022, showing some inter-annual variability. The consistently negative water budget indicates that evapotranspiration exceeds precipitation each year. This implies a deficit in water availability, meaning more water is being lost than gained. The deficit suggests that additional sources, such as groundwater or external water supplies, might be necessary to meet the water demand. The fluctuations in the water budget could be attributed to specific climatic events, such as unusually dry or wet years, influencing the balance between precipitation and evapotranspiration. For instance, a lower water budget in 2016 might indicate a particularly dry year or increased evapotranspiration due to higher temperatures.

The graph 2(b) illustrates the monthly averages for precipitation, evapotranspiration, and the water budget in Germany over the period from 2013 to 2022. Precipitation remains relatively constant throughout the year, with slight increases during the spring and summer months. The values range from approximately 2 mm/month in the winter months to around 5 mm/month in the summer months. Evapotranspiration shows a clear seasonal pattern, increasing significantly during the warmer months. The highest values are observed in June and July, reaching up to 25 mm/month. During the colder months (November to February), evapotranspiration is minimal, around 2-3 mm/month.

The water budget, defined as P - ET, indicates the net balance between precipitation and evapotranspiration. The values are positive in the colder months (October to April), suggesting that precipitation exceeds evapotranspiration. The values become negative from May to September, indicating that evapotranspiration exceeds precipitation during these warmer months. The most significant negative water budget is observed in June, reaching around -20 mm/month. Spring and Summer: During these months, the increased temperature leads to higher evapotranspiration, which significantly exceeds precipitation, resulting in a negative water budget. This indicates a higher demand for water and potential water deficits. Fall and Winter: The cooler temperatures reduce evapotranspiration, and precipitation slightly increases or remains constant, leading to a positive water budget. This suggests a period of water surplus where precipitation exceeds water loss.

CONCLUSION

This project conducted a comprehensive spatial analysis of evapotranspiration (ET) and precipitation (P) to study the water balance in Germany from 2013 to 2022. Annual data revealed stable patterns for both ET and P, but with a consistently negative water budget, indicating that ET exceeded P each year. Monthly analysis showed significant seasonal variability, with a pronounced negative water budget during the warmer months (May to September) and a positive budget during the colder months (October to April). Spatial analysis identified regional disparities, with northern and coastal regions receiving more precipitation and southern and inland areas experiencing higher ET rates. These findings underscore the need for region-specific and adaptive water management strategies to address the persistent water deficit and seasonal fluctuations. The insights from this study are crucial for informing water conservation, efficient irrigation, and seasonal storage practices to ensure sustainable water availability across Germany in the face of climate variability and change.

References:

Jung, M., et al. (2010). "Recent decline in the global land evapotranspiration trend due to limited moisture supply." Nature, 467(7318), 951-954. doi:10.1038/nature09396
Mueller, B., et al. (2011). "Evaluation of global observations-based evapotranspiration datasets and IPCC AR4 simulations." Geophysical Research Letters, 38(6). doi:10.1029/2010GL046230
Fischer, E. M., et al. (2013). "Climate change impacts on European crop yields are highly heterogeneous." Nature Communications, 4, 2535. doi:10.1038/ncomms3535
Zolina, O., et al. (2008). "Changes in the duration of European wet and dry spells during the last 60 years." Journal of Climate, 21(13), 1744-1765. doi:10.1175/2007JCLI2065.1
Maraun, D., et al. (2010). "Precipitation downscaling under climate change: Recent developments to bridge the gap between dynamical models and the end user." Reviews of Geophysics, 48(3). doi:10.1029/2009RG000314
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Huntington, T. G. (2006). "Evidence for intensification of the global water cycle: Review and synthesis." Journal of Hydrology, 319(1-4), 83-95. doi:10.1016/j.jhydrol.2005.07.003