Effect of Land Cover Change and Deforestation Around Maninjau Lake on Rainfall and Surface Temperature

Fish deaths in Maninjau Lake have been frequently reported. Apart from fishery activities, this can also be caused by changes in atmospheric conditions around Lake Maninjau due to changes in land cover around Lake Maninjau. Therefore, this study analyzes land cover changes and deforestation in 2001 and 2020 and their relationships with surface temperature and rainfall. Rainfall data and extreme temperatures were obtained from the Integrated Multi-satellite Retrievals for GPM (IMERG) and ECMWF v5 (ERA5), respectively. Land cover data based on the Landsat satellite is used to see land changes. The results showed a decrease in the amount of vegetated land every year and an increase in residential and building land and agricultural land, which correlates with an increase in the surface temperature in the Maninjau area. Furthermore, the results also show a coherent relationship between rainfall trends and areas of deforestation.


Introduction
Land cover change influences climate change.Recently, global climate change has become a concern for the world community [1].Climate change causes an increase in water temperature, rainfall changes, frequency and intensity of storms, and others.The impact of climate change has a profound effect on human life, especially on fisheries production and fish biodiversity [2][3].
Lake Maninjau in West Sumatra is a lake with a very high utilization rate in both land and water areas [4].Mass deaths of fish often occur in Maninjau lakes.Mass fish deaths first occurred in 1997, as many as 950 tons.Subsequent mass deaths occurred in early January 2009, and the most recent mass deaths in December 2021 fish deaths reached 1,646 tons.According to the Marine and Fisheries Service of West Sumatra Province, the cause of fish death in Lake Maninjau was due to upwelling and lake water.These mass deaths are spurred by climate change, which has recently seen many strong winds over the waters, both from the north and south of the lake area.The strong winds caused waves accompanied by the potential for excess fish feed given to aquaculture activities to cause an "up-welling" phenomenon in these waters.Mass death of fish results in economic losses and has a social impact directly and indirectly on fish farming communities and other communities [5].
From the previous discussion, it is interesting to look at the problem of climate change with cases of fish deaths due to land cover change and deforestation in 2001 and 2020 in the area around Lake Maninjau.This study used Landsat 5 TM, 7 ETM +, and 8 OLI satellite data and surface temperature.This method was chosen because it is more effective in collecting data in the form of secondary data from satellite imagery.

Data and Methodology
We classified the land cover change into four classes: vegetation, agricultural land, built-up land, and water bodies.Integrated Multi-satellitE Retrievals for GPM (IMERG) satellite is used as rain data and extreme temperatures was obtained from ECMWF Reanalysis v5 (ERA5).Several researchers have evaluated the accuracy of the IMERG data in Indonesia [6,7].We used IMERG version 06 with the lowest value considered to be rain for IMERG products is 0.2 mm h −1 [7].

Land Cover Classification
The classification of land cover is carried out using the maximum likelihood method.Classification begins with making a training area for each land cover category using ROI (Regions of Interest) [8].The classification was done using a combination of bands on Landsat 8 OLI, 6 5 4 (vegetation analyst), while Landsat 7 ETM+ and 5 TM, the band combination is used 5 4 3 (vegetation analyst).Analysis of land use change was carried out by comparing land change maps for 2000-2019, which have been validated using the GIS overlay analysis method.

Changes in rainfall and extreme temperatures
The increase in rain occurrence was analyzed based on rain event data recorded by the IMERG in Indonesia in 2001, 2004, 2008, 2012, 2016, and 2020.Meanwhile, the temperature data used is daily data on maximum temperature and minimum temperature in the 2000-2019 period.The data is processed to see temperature changes and determine the index of extreme conditions.The Expert Team on Climate Change Detection and Indices (ETCCDI) Index was used as extreme index in this study.

Land cover change
Table 1 shows changes in the land cover area from 2001 to 2020 for four classes of land cover in the Maninjau Lake area.A decreasing trend in vegetation areas was observed.This trend follows the increase in built-up land and agricultural land in the Maninjau area.The spatial distribution of the changes in cover in 2001,2004,2008,2012,2016, and 2020 are found in Figures 1, Figure 2, Figure 3, Figure 4, Figure 5, and Figure 6.The most substantial decrease in the number of vegetation areas around the Maninjau Lake area occurred in 2020.The change of land from vegetation to agricultural land is most significant.This is related to community activities in the Maninjau Lake area.Most of the land used by the community around the lake is paddy fields and plantations.The Maninjau area is dominated by a stretch of settled farming area, which consists of two primary forms.First, rice cultivation in irrigated rice fields is scattered on the lake terraces and slope bottoms, including 13 to 75% of rural farmland (or 3.5 to 30% of rural land) [9].
Rice farming and plantations are the main activities carried out after going to the lake because most of the land around the lake has been converted from forests, especially those without steep marbles, into rice fields and gardens.The primary commodities around Maninjau lake are rice and other commodities      The increase in the number of built-up lands in the Maninjau Lake area is closely related to the increase in residents in the region.Figures 5 and 6 show the highest spread of built-up land from agricultural areas, around 2069.46 Ha of agricultural areas turned into built-up land.

Relationship of land cover change with rain and temperature
Figure 7 shows the distribution of surface temperatures in the Maninjau Lake area from ERA5 data.The largest average temperature occurred in 2020, with a temperature value of 300 K.Meanwhile, the lowest average temperature occurred in 2008 at 299.2 K. Changes in temperature with changes in land cover can be seen in Figure 8.A lower temperature was observed in regions with a high amount of vegetation.In 2001, vegetation area of 2,185.74Ha result in the average surface temperature was 299.9 K.The results of the classification of land cover in the form of agricultural land and vegetation in 2016 were mostly turned into settlements in 2020.It can be seen from this pattern of distribution and land cover change that land change in the form of vegetation has a temperature influence in this study because, with the growth of built-up land increases, the surface temperature also increases.This contrasts with solar radiation escaping on the surface controlled by surface shortwave albedo.Changes in surface albedo result from land cover type change [11].Different heat capacities for different land cover, may also result in different temperature [12].The change in annual rainfall in the Lake Maninjau area is given in Figure 9.The largest annual rainfall is observed during 2008.Such high rainfall is related to a decrease in temperature due to an increase in the amount of agricultural land.It causes an increase in the area of water bodies in the Maninjau Lake area.Meanwhile, the lowest rainfall occurred in 2000 at 2641.05 mm/year, with the highest vegetation area in the observation year.

Conclusion
This study shows a change in land cover around Lake Maninjau from 2001 to 2020.The built-up land area has increased yearly; the widest cover was observed in 2020.Changes in land use such as built-up land and agricultural land, resulted in an increase in surface temperature.The relationship between surface temperature and vegetation region is inversely proportional.Meanwhile, the relationship between land cover change and rainfall is not so apparent around Lake Maninjau.

Figure 1 .
Figure 1.Land cover map of the Maninjau Lake area in 2001.

Figure 2 .
Figure 2. Land cover map of the Maninjau Lake area in 2004.The increase in the number of built-up land areas in 2004 occurred in agricultural areas of 1420.65 Ha and from vegetation areas of 12.78 Ha.Meanwhile, in 2008 401.94 ha of agricultural area was turned into built-up land.This is due to an increase in the number of residents around the Maninjau Lake area.

Figure 3 .
Figure 3. Land cover map of the Maninjau Lake area in 2008.

Figure 4 .
Figure 4. Land cover map of the Maninjau Lake area in 2012.

Figure 5 .
Figure 5. Land cover map of the Maninjau Lake area in 2016

Figure 6 .
Figure 6.Land cover map of the Maninjau Lake area in 2020.

Figure 8 .
Figure 8. Relationship of land cover to temperature.

Figure 9 .
Figure 9. Relationship of land cover to rainfall.

Table 1 .
Land cover area of Lake Maninjau (Ha) area.