Nile discharge dynamics, large-scale teleconnection and climate
Abstract
Nile river, which floods during summer annually, is vital to local agriculture
from ancient times. Precipitation originating from Ethiopian and equatorial Eastern African high lands collects in the Nile river and flows downstream. Combining with the spatial structure of the river including elevations and local catchments, the inflow of the Nile shows strong seasonality, starting to increase from June and maximising near the end of summer. Tropical precipitation over equatorial east Africa highlands varies on a wide range of timescales, including intraseasonal, interannual and decadal time-scales, which is reflected in the river inflow. In this research, we introduce a periodic nonautonomous stochastic model constructed from a monthly-averaged inflow data measured at Aswan high dam spanning from 1871 to 2002. The model provides a physical explanation of the mechanism of the seasonal inundation using the interaction between seasonal stability and noise forcing, which is found to be quite similar to the seasonal evolution of climate positive feedbacks such as sea ice albedo and Bjerknes feedbacks. At the same time, it enables us to trace back the history of the Nile discharge related to the construction of Aswan low and high dams. It is shown, in particular, that the dams stabilise the positive feedback, which occurs during summer in the absence of dams, likely due to the dramatic change of the river morphology. The constructed long-term forcing suggests the strong connection with ENSO and the decadal variability of ocean circulation such as Pacific Decadal Oscillation. Potential use of the model in inflow forecasting is discussed.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC21G1356M
- Keywords:
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- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 1812 Drought;
- HYDROLOGY;
- 1821 Floods;
- HYDROLOGY