Impacts of Land Use and Land Cover Change

Southern Asia, predominantly the Indian subcontinent region, has shown dramatic land use land cover changes in recent times in response to the growing food and fiber requirements of a fast increasing population (Foley et al., 2005). Landscape changes in the region, in recent decades, has primarily occurred because of urbanisation (Kishtawal et al., 2010) and intensive agriculture/irrigation practices (Douglas et al., 2009). Such changes are illustrated through population changes in figure 1. Recent research has illustrated that human-induced landscape changes can affect atmospheric processes from local to regional weather patterns (Cotton and Pielke, 2007; Alpert et al., 2006) and climate variability (Pielke et al., 2007; National Research Council, 2005). Subsequently this post will look to summarise 3 journals illustrating these impacts.

Figure 1. (a) Population of India form 1901 to 2001 based on official census reports. (b) Density of population
(persons per square kilometre, values shown are natural log of actual numbers) over the Indian summer
monsoon region for the year 2000. (c) Difference of the density of population (natural log of numbers shown)
between the years 1990 and 2000. Source: Niyogi et al., (2010). p. 2.

The first was produced by Niyogi et al., (2010). Using satellite data the authors attempted to link daily rainfall observations with monthly satellite land surface data, to illustrate the connection between land use change and monsoonal rainfall. Using genetic algorithms (GA), empirical orthogonal functions (EOF), and causal discovery algorithms (CDA) a range of patterns were identified. Firstly, the EOF and GA analysis identified decreasing rainfall in the monsoon season in north/northwest India, which coincided with regions of agricultural intensive land use but highlighted further analysed is required. Additionally, correlations and the CDA suggest that pre-monsoon (March-April) vegetation affects July month precipitation over Peninsular India. In particular, a negative relationship exists. These results suggest that an increase in agriculture has possibly weakened the early monsoon rainfall. The journal highlights how agricultural intensification could be reducing summer monsoon rainfall over certain regions of India.

Douglas et al., (2006) have focused on changes in irrigation on land-atmosphere interactions and Indian monsoon precipitation. Douglas et al used the Regional Atmospheric Modelling System (RAMS). Four scenarios were adopted: (1) a control – observed NDVI (satellite measure of vegetation productivity); (2) irrigated crop scenario; (3) non-irrigated crop scenario; and (4) a scenario of natural vegetation growth. The model indicated that under active monsoon conditions, surface energy and moisture flux over India are sensitive to irrigation intensity and this effect is more pronounced than the other scenarios. Irrigation was proven to increase moisture flux, which in turn modified the convective potential energy. This caused a reduction in the surface temperature and led to a modified regional circulation pattern and changes in mesoscale precipitation.

Similarly to Douglas et al., Lee et al., (2009) focused on the effects of irrigation but relied upon observational data like Niyogi et al., (2010). The authors examined the effects of land cover change over the Indian subcontinent during pre-monsoon season (March, April and May - MAM) on early summer monsoon rainfall using NDVI and July precipitation between 1982 and 2003. MAM NDVI has increased and the increases are significantly correlated with increases in the irrigated area, not preceding rainfall. July rainfall significantly decreased in central and southern India, and the decrease is statistically related to the increase in the preceding MAM NDVI. The authors highlight that decreased July surface temperatures (an expected result of increased evapotranspiration due to irrigation and increased vegetation) leads to a reduced land-sea thermal contrast, which is one of the factors driving the monsoon, and therefore weakens the monsoon circulation. A weak early monsoon is partially a result of irrigation and the resultant increased vegetation and crop activity prior to the monsoon.

The 3 journals reviewed here use statistical evidence to suggest increased land cover land use change is weakening parts of the Indian monsoon. Importantly, each journal highlights that results are more robust over northern and Peninsular India; so further research is required to understand the impacts in different regions. At a socio-economic level the research illustrates how unsustainable, increase in agricultural intensification may begin to have a negative feedback and the relationships proved throughout the research should be a primary focus of future climate simulations, particularly throughout India. 

The 3 main References:

Douglas, E., Niyogi, D., Frolking, S., Yeluripati, J., Pielke, A., Niyogi, N., Vorosmarty, C. and Mohanty, U. (2006) Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indina Monsoon Belt. Geophysical Research Letters. 33:1-5.

Lee, E., Chase, T., Rajagopalan, B., Barry, R., Wiggs, T. and Lawrence, P. (2009) Effects of irrigation and vegetation activity on early Indian summer monsoon variability. International Journal of Climatology. 29: 573-581. 

Niyogi, D., Kishtawal, C., Tripathi, S. and Govindaraju, R. (2010) Observational evidence that agricultural intensification and land use change may be reducing the Indian summer monsoon rainfall. Water Resources Research. 46: 1-17. 

See each journal for other references used.