A GIS based approach for assessing water body change in a mountain wetland: case of Dayet Awwa, Morocco

. According to the definition derived from the International Convention on Wetlands (Ramsar), wetlands are areas that cover a wide range of habitat types, including floodplains, marshes, streams, estuaries and offshore coastal areas. These natural habitats provide a variety of ecosystem services, for instance, they contribute to mitigate the impacts of climate change. Nevertheless, one of the most critical issues of our time is that mountain wetlands are particularly threatened by many changes, which have a profound impact on their ecosystem services. Hence, the main goal of this work in the Middle Atlas (Morocco), using a GIS based approach is to emphasize the threat to wetlands and their ecosystem services. In this study, Landsat satellite imagery is used to calculate the NDWI (Normalized Difference Water Index) for the lake dayet Awwa. The calculation results show that the surface area of the lake has decreased significantly between the years 1985 and 2018. This decline can be explained by natural and anthropogenic factors.


Introduction
Whether it's an oasis or a river, a coastal marsh or a pond, life begins in wetlands.In fact, 40% of the world's flora and fauna depend on freshwater wetlands, which protect against floods and droughts and purify water.But wetlands are at breaking point, and we are losing them three times faster than we are losing forests, pushing many species towards extinction and causing extreme weather conditions.
As defined by the International Convention on Wetlands (Ramsar), wetlands are areas that cover a wide range of habitat types, including floodplains, marshes, rivers, estuaries and offshore coastal areas [4].
There are currently more than 2300 Ramsar Sites covering an area of over 2, 500,000 Km 2 [13].These ecosystems cover around 6% of the earth's surface and are known to be home to more than 10,000 species of fish and over 4,000 species of amphibians [3].Wetlands provide numerous ecosystem services, including cultural services, provisioning services and regulating services such as carbon sequestration, water purification and flow regulation [12].
Nevertheless, according to the IPCC report (2007), wetlands are among the most vulnerable ecosystems to climate change, with degradation and loss occurring faster than any other ecosystem [7].According to Davidson [6], 87% of wetlands have been lost since 1700 [11].As a result, the rate of wetland loss is estimated to have increased by 0.78% per year since 1990, due to rapid transformation, pollution and fragmentation [6,5].In the Middle Atlas, the number and surface area of these ecosystems have declined significantly over the last forty years [2].In addition to climate change impacts, mountain wetlands in Morocco face several threats, including pollution, overgrazing, overexploitation of resources, disturbance of wildlife and drying out.Anthropogenic activities, like agricultural extension, encroachment of built-up land, hydrological modification, and discharge of pollutants are contributing to wetlands degradation [1].
The aim of the present study is to develop a methodology based on the use of geospatial data to assess changes in water body in one of the most important mountain wetlands in Morocco.Geospatial data and model simulations will be used to establish an up-to-date reference situation for the dynamics of this wetland.

Study area
The Dayet Awwa water lake (33°39'07'' N, 05°02'07'' W) (Fig 1), is located in the western part of the Middle Atlas.This lake is located at an altitude of 1510 m, 15 km north of Ifrane and 10 km south of the village of Imouzzer Kandar.It is the most famous lake in Morocco [12].This wetland is made up of low-lying wet grassland and holm oak and cedar forests, and is surrounded by a belt of poplar and a few willow trees on its immediate edges.Dayet Awwa is a limnic ecosystem with a very high level of biodiversity.It is one of the Middle Atlas lakes with the most diverse fauna.This ecosystem is a wintering and nesting place for water birds.Dayet Awwa is also a bird-watching area for many national and international ornithologists [15].

Methodology
Using GIS tools to monitor wetland water body change is of major importance given the lack of timely qualitative and quantitative information.Thus satellite-based information is able to fill information gaps and contributes to planning, management and reporting by users and decision-makers [13].Satellite imagery is used to derive basic information on the quality of wetland ecosystems, diagnose threats and pressures on wetlands, monitor changes in extent and condition, and inform better management.Adopting an approach based on the use of geospatial data, we first calculate the normal deviation index   and the image index NDWI.

Normal deviation index 𝑬 𝒏
This index, also known as the rainfall deficit index, makes it possible to visualise and determine the number of deficit years and their sequence.It is expressed as: is the rainfall in year i for the given period and   is the normal rainfall for the same period.This index provides a point estimate of precipitation in relation to the normal (a year is classified as dry if rainfall is below normal).In our case, the comparison can only be made if the climatic conditions of the years studied are similar.The selected years, 1985, 2008 and 2018, are normal years.

Normalized Difference Water Index
The calculation was carried out for the years 1985, 2008 and 2018 by importing Landsat 5 satellite images from the USGS Earth Explorer data portal.All the satellite images were obtained for the month of September.Then the NDWI (Normalized Difference Water Index) was calculated.
This index is generally used to monitor changes in water content in water bodies, using the green and NIR spectral bands.It was introduced by McFeeters (2013) and calculated as follows: Where: NIR: pixel values in the near infrared channel Green: pixel values in the green channel.
Water features have positive NDWI values, while soil and terrestrial vegetation tend to have negative values [9].
Values of water bodies are larger than 0,5 .Since the vegetation has much smaller values, it is easier to distinguish vegetation from water bodies easier.Built-up features have positive values between 0 and 0,2 (Table 1).

Results
For the year 1985, NDWI values reach 0.5.This proves the existence of water surface in large quantities (  -Climate change Morocco is facing increased vulnerability to climate change, and is considered to be a "climate hotspot" [10].More specifically, in the Middle Atlas, average annual data shows a warming of around 1.5°C in 50 years and a significant drop in rainfall since the end of the 1970s [8].Unfortunately, these trends are set to worsen over the coming decades [10].In the same context, Dayet Awwa is a lake that is highly sensitive to the effects of climatic conditions.The lake's water potential is affected by recurrent periods of drought in the region.[15] -Land use change Land use change is the result of more than 30 years of intensive agriculture in the study area.It includes 6,806 hectares of utilized agricultural area and 1,654 farms in 2022 (Fig 5).The extension of vast areas of different crops lead to the exhaustion of groundwater because of excessive well drilling .This, had a negative impact on the hydrological regime and, consequently, on water levels in the Lake.The impoundment of dams remains a significant factor contributing to the drying up of the lake.
The increase in storage infrastructure through the construction of dams, hill reservoirs or agricultural ponds has an impact on the hydrological functioning of the watersheds concerned.On a socio-economic level, the total drying up of the lake is affecting the incomegenerating activities of the population [15].Considering that the activity rate in the study area does not exceed 33% [14].As a result, many of the 9,854 local residents living along the shores of the lake suffer from unemployment, which is often the main reason for the rural exodus [15].

Conclusion
According to the definition derived from the International Convention on Wetlands (Ramsar), wetlands are areas of high importance that cover a wide range of habitat types.
Wetland ecosystems provide undeniable services.Thus, they play a crucial role in sustainable development.Consequently, the rational management of these areas is becoming essential.However, in Morocco as elsewhere in the world, these areas face a number of natural and man-made threats.Therefore, this study is of utmost importance, providing a better understanding of the dynamics of change in water body at Lake Dayet Awwa in the Moroccan Middle Atlas, using geospatial data.
Calculating the NDWI (Normalized Difference Water Index) confirms the lake's complete dryness.In the light of the results obtained, a multidisciplinary analysis was carried out to identify the factors contributing to this drought and the impacts it is having.In fact, climate change and land use change are major factors.This work is part of an integral vision whose ultimate objective is to contribute effectively to presenting new perspectives on the management of wetlands, which play an undeniable role in mitigating the impacts of climate change.
It is recognised that adequate protection and wise use of wetlands is a key element of any climate strategy, and that restoration is necessary when these sites have been degraded.Hence, this work helps to broaden water managers' knowledge of the importance of protecting and restoring wetlands.

Fig. 1 .
Fig. 1.Location of the Dayet Awwa site[15] Fig 2).NDWI values for the year 2018 vary from -0.4 to 0.1, indicating the absence of water surfaces (Fig3).And that means that the lake is dry, this is confirmed in the field (Fig 4); Calculating NDWI enables to conclude that water body has significantly decreased since 1985; This change is due to the combined effect of anthropogenic factors and climate change.

Fig. 5 ..
Fig. 5 . .Extensive apple trees surfaces in the vicinity of the lake

Table 1 .
Ranges corresponding of NDWI values