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Messages - Ila Chawla

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Interesting information / The Effects of Tropical Vegetation On Rainfall
« on: August 14, 2018, 10:58:27 PM »
Vegetation modifies land-surface properties, mediating the exchange of energy, moisture, trace gases, and aerosols between the land and the atmosphere. These exchanges influence the atmosphere on local, regional, and global scales. Through altering surface properties, vegetation change can impact on weather and climate. We review current understanding of the processes through which tropical land-cover change (LCC) affects rainfall. Tropical deforestation leads to reduced evapotranspiration, increasing surface temperatures by 1–3 K and causing boundary layer circulations, which in turn increase rainfall over some regions and reduce it elsewhere. On larger scales, deforestation leads to reductions in moisture recycling, reducing regional rainfall by up to 40%. Impacts of future tropical LCC on rainfall are uncertain but could be of similar magnitude to those caused by climate change. Climate and sustainable development policies need to account for the impacts of tropical LCC on local and regional rainfall.


Link to paper: https://www.annualreviews.org/doi/abs/10.1146/annurev-environ-102017-030136
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2
In recent decades India has undergone substantial land use/land cover change as a result of population growth and economic development. Historical land use/land cover maps are necessary to quantify the impact of change at global and regional scales, improve predictions about the quantity and location of future change and support planning decisions. Here, a regional land use change model driven by district-level inventory data is used to generate an annual time series of high-resolution gridded land use/land cover maps for the Indian subcontinent between 1960–2010. The allocation procedure is based on statistical analysis of the relationship between contemporary land use/land cover and various spatially explicit covariates. A comparison of the simulated map for 1985 against remotely-sensed land use/land cover maps for 1985 and 2005 reveals considerable discrepancy between the simulated and remote sensing maps, much of which arises due to differences in the amount of land use/land cover change between the inventory data and the remote sensing maps.


Link to paper: https://www.nature.com/articles/sdata2018159


Link to data: https://figshare.com/collections/A_spatio-temporal_land_use_land_cover_reconstruction_for_India_1960_2010_/3967329
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3
Models / Re: Anybody working with VIC model
« on: June 16, 2016, 02:46:27 PM »
I would like to add some more information to this post. From personal communication with Sat I could learn the manner in which flow direction map should be prepared and I would like to summarize the findings here.

Once the flow direction map is prepared, though a tedious job in case of huge basins, one has to visualize how the flow is taking place from one cell to other. Say I have following 3 by 3 cells encompassing my basin.
1 1 0
1 1 0
0 0 1
where, 1 indicates locations where basin is situated and cell(3,3) is the outlet (indicating all the water in basin should drain to this cell). Let us assume we got following flow direction map.
5 7 0
5 1 0
0 0 1
where, the numbers indicate the directions provided in http://vic.readthedocs.io/en/vic.4.2.c/Documentation/Routing/FlowDirection/

If you observe cell(2,1) the flow direction, which is 5, is showing that the water is flowing outwards (south direction). And cell(2,2) has north direction. It can be observed that these numbers will form an eternal loop of water flow without it ever reaching cell(3,3). This could lead to an error while executing routing model, more specifically, "Searching for catchment" issue.
I would expect the cell(2,1)'s direction to be 3 (towards east) and cell(2,2)'s direction to be 4 (south-east towards cell (3,3)) which gives the following flow direction file.
5 7 0
3 4 0
0 0 1

Now if we visualize the flow of water from cell to cell, we can observe that water from all the cells finally reaches cell(3,3). Thank you Sat for helping me understand this very sensible concept.
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