# How Will Rwandan Land Use/Land Cover Change under High Population Pressure and Changing Climate?
## 4 Discussion
### Analysis of Factors Driving Land Use Change  
The area of forest, grassland, and cropland changed over time, and the factors driving this change in area have also changed gradually. In Rwanda, changes in forest, grassland, and cropland were driven by multiple factors, while changes in wetlands, waters, urban land, and unused land were driven to a greater degree by a single factor than the first three. In 2010 (from Phase B to C), the driving factor of forest changed from 'precipitation--population' to 'topography--population'. This change indicated that precipitation was no longer the main factor limiting the change in forest land. Instead, topography and the high population pressure together drove the change in forest. In East Africa, population was the main factor driving LULC change, but the main factor driving forest change did not change to population [6]. This is because low-altitude, scattered forest patches were gradually converted into cropland. Most of the newly added forest land was located in high-altitude areas that were not suitable for human habitation, or in areas such as nature reserves (Nyungwe Forest National Park); population pressure could not be expressed effectively in areas with few people. Moreover, Rwanda has a temperate tropical plateau climate with abundant rainfall and rapid vegetation growth, so precipitation became the main driving factor. The driving factor of grassland changed from 'population--topography' to 'precipitation--population'. Under high population pressure, grassland suitable for cultivation was transferred to cropland (Table A2). Therefore, during Phases A and B, population was the main factor driving grassland change, and topography was the factor limiting the expansion of grassland. Owing to the lack of sustainable land management measures, part of the cropland underwent severe deterioration and was abandoned because it was unsuitable for cultivation (Table A3). After a short period of natural succession, the vegetation in these abandoned cropland areas was restored to grassland vegetation. The natural succession of grasslands was mostly observed in areas with abundant rainfall and dense populations. Therefore, precipitation and population became the new driving forces for grassland change. The driving factor of cropland changed from 'population--topography' to 'population--precipitation'. Owing to the increase in population pressure, croplands gradually expanded. The expansion of cropland caused a reduction in the forest distributed in high-altitude and high-latitude areas. The topography could no longer limit the expansion of cropland, and thus, topography was no longer the main factor restricting the expansion of cropland. Furthermore, owing to the increase in the elevation of cropland, which was more abundant in the high-altitude areas of Rwanda, precipitation replaced population as the main factor driving cropland change. Wetlands were primarily distributed along river courses, and were therefore primarily found in the low-altitude and relatively flat eastern regions with developed water systems; the fluctuations to their area were small. Thus, topography was the main factor limiting wetland changes. The driving factor of water area changed from 'topography--population' to 'location--topography'. Rwanda's water bodies are primarily natural rivers and lakes, which serve as the sources of water used by Rwandans for various activities. Thus, the change in water area is driven by the population. [47]. The cropland in the river valleys is also an important part of the arable land in Rwanda. Rwanda receives abundant rainfall and frequent heavy rains during the rainy seasons, which raises level of water in its rivers. The existence of drainage measures maintains the stability of the arable land area in the river valleys.