; Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
Fig. 4. Comparison of Hydrograph at main outlet (Mundali): 
Calibration period 
the period of 1972-85 and 7.47 mm in 1985-03) which is 4.53% 
of the flow in 1972. It may be concluded that a decrease in 
forest cover by 5.71% in the Mahanadi river basin has caused 
the river flow to increase by 4.53%. This is quite a significant 
amount in terms of volumetric rise (3514242122 m 3 ). Table 2 
summarizes the predicted incremental changes in runoff (mm) 
at outlet by season (e.g. JFM refers to cumulative rise for 
January, February and March). In figure 7, monthly 
hydrographs for 1972 and 2003 are presented to see the changes 
that have taken place. A plot of relative percentage difference in 
runoff (from 1972 to 2003) over 1972 is also shown in the same 
figure. The rise in percent runoff was prominent during May, 
June, Oct and November months. The decrease in runoff from 
1972 to 2003 may be due to reverse trend in landcover 
conversions and/or human activities. 
Though the agreement between observed and simulated 
discharges is good, under-estimations and over-estimations are 
inherent in the simulation. This is because of the fact that VIC 
simulates naturalized flows and the observed discharge used for 
validation is biased and affected by human interventions. Model 
performance showed good agreement at Mundali inspite of a 
large reservoir since calibration was performed at this outlet. It 
may be seen from the simulation results that model has 
generally overestimated (S>0) during months of June, July and 
under-estimated during August and September. The possible 
reason may be initial reservoir storage in June-July due to which 
observed flows are less as compared to simulated whereas 
observed flow exceeds once the reservoir capacity is filled (in 
Aug, Sept.). It may be concluded that the agreement between 
and observed and simulated hydrological components is largely 
dependent on the hydrological and landcover conditions in the 
basin and model assumptions. The synoptic view and 
landuse/landcover conditions of various sub-basins are shown in 
the Figure 2. The landcover classes are same as shown for 
whole of the Mahanadi basin (Fig. 1) with Mundali as an outlet. 
Fig. 5. Simulated and observed monthly hydrographs at outlet 
In summary, a decrease in natural cover of forest over time has 
caused a significant rise in streamflows and particularly surface 
runoff. Removal of forest cover is known to increase 
streamflow as a result of reduced évapotranspiration. Base-flow 
is expected to decrease while surface runoff increases owing to 
the decrease in infiltration and hence groundwater recharge 
processes. Urban expansion and intensive cultivation will 
loosen the soil leading to soil loss (soil erosion) due to high 
flows. Urbanization also tends to decrease infiltration rates and 
increase extents of impervious surfaces, although the area over 
which such changes have occurred is a small fraction of the 
total basin area. The VIC model, being physically based, 
distributed, macroscale model is particularly suitable for 
studying climate and landcover change scenarios and their 
implications on hydrological processes at regional and global 
scale over long time frames. 
Q-1972 
4.2 Effect of landcover changes on streamflows 
4.2.1 Historical and current hydrological simulation using 
VIC model: Simulation was done for year 1972 and 1985 after 
calibration and validation of the VIC model for 2003. Only the 
vegetation cover and related parameters were changed in the 
simulations; the model meteorological forcings and soil 
parameters were kept same for both the current and historical 
scenarios. In this way, the effects of vegetation change on basin 
hydrology were isolated from the effects of climate variability. 
4.2.2 Trend of changes in streamflows: Streamflows for year 
1972, 1985 and 2003 were compared to look for the changes 
that have taken place due to change in landcover in the 
Mahanadi river basin. Monthly discharges were found to be 
varying significantly as compared to daily flows. Fig 6 shows a 
scatter plot of monthly flows (mm) for 2003 and 1972, events 
above the slope line indicates an increase in river flow. A rise of 
24.44 mm in the annual discharge is predicted at Mundali outlet 
of the Mahanadi basin from 1972 to 2003 (16.97 mm being in 
Fig.6. Comparison of streamflows for 1972-2003 at Mundali 
Table 2. Changes in runoff by sub-basin and season (in mm) 
Stations 
JFM 
AMJ 
JAS 
OND 
Annu 
al 
% 
increa 
se 
j | of? 
Mundali 
0.027 
1.79 
16.97 
5.64 
24.44 
4.53 
3.51 x 
10 6