10 Hydrology and Climate Impacts on Streamflow and Sediment …
229
y = 0.3203x + 1008.4
R² = 0.4766
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0
500
1000
1500
2000
River Discharge (m 3
/day)
Rainfall (mm/year)
Fig. 8 Relationship between total annual rainfall and annual river discharge in the Nyando River,
1956–1974
4.3 Relationship Between Rainfall and River Discharge
The relationship between rainfall and river discharge in the Nyando River Basin is
complex. Data for the period 1956–1974 yield a correlation coefficient r of 0.71
with a coefficient of determination R
2 of 0.51. The relationship between rainfall
and streamflow in the basin established using 2003–2012 data yield a R
2 of 0.63
and correlation coefficient r of 0.80. These results could be interpreted to indicate
that rainfall in the Nyando River Basin explains 51%–63% of the variation in river
discharge. Therefore, in addition to rainfall, catchment characteristics could also be
contributing to variation in river discharge. These catchment characteristics include
land use, vegetation cover, and topography. The results also show that there exists a
strong relationship between rainfall and river discharge in the Nyando Basin (Fig. 8).
An increase in rainfall in the basin therefore leads to a corresponding increasing in
river discharge.
4.4 River Discharge and Rainfall Deficits
Rainfall and river discharge deficits were computed as the difference between
monthly values and long-term mean values. Figure 9 shows rainfall and river
discharge deficit from 2003 to 2012 at RGS IGD03, which indicate that river
discharge was above the long-term mean value 16 times. River discharge was also
below the long-term mean value 16 times. However, the magnitude of above-average
flows seems to be much higher than the below-average river discharge. Aboveaverage flows normally last four to eight months, and below-average flows last about
the same.
229
y = 0.3203x + 1008.4
R² = 0.4766
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0
500
1000
1500
2000
River Discharge (m 3
/day)
Rainfall (mm/year)
Fig. 8 Relationship between total annual rainfall and annual river discharge in the Nyando River,
1956–1974
4.3 Relationship Between Rainfall and River Discharge
The relationship between rainfall and river discharge in the Nyando River Basin is
complex. Data for the period 1956–1974 yield a correlation coefficient r of 0.71
with a coefficient of determination R
2 of 0.51. The relationship between rainfall
and streamflow in the basin established using 2003–2012 data yield a R
2 of 0.63
and correlation coefficient r of 0.80. These results could be interpreted to indicate
that rainfall in the Nyando River Basin explains 51%–63% of the variation in river
discharge. Therefore, in addition to rainfall, catchment characteristics could also be
contributing to variation in river discharge. These catchment characteristics include
land use, vegetation cover, and topography. The results also show that there exists a
strong relationship between rainfall and river discharge in the Nyando Basin (Fig. 8).
An increase in rainfall in the basin therefore leads to a corresponding increasing in
river discharge.
4.4 River Discharge and Rainfall Deficits
Rainfall and river discharge deficits were computed as the difference between
monthly values and long-term mean values. Figure 9 shows rainfall and river
discharge deficit from 2003 to 2012 at RGS IGD03, which indicate that river
discharge was above the long-term mean value 16 times. River discharge was also
below the long-term mean value 16 times. However, the magnitude of above-average
flows seems to be much higher than the below-average river discharge. Aboveaverage flows normally last four to eight months, and below-average flows last about
the same.