Prediction of seasonal runoff in ungauged basins - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 103

400 400 400

Beles
3431 km²

Megech
462 km²

Ribb
1592 km²

300 300 300

200 200 200

100 100 100

0 0 0

JFMAM JJASOND JFMAM JJASOND JFMAM JJASOND

400 400

Birr
978 km²

Gumera
1394 km²

300 300

200 200

100

100

0

0

JFMAM JJASOND

JFMAM JJASOND

400 400

Andassa
573 km²

Abelti
15756 km²

300 300

200

200

100

100

200 km

0

0

JFMA M

JFMAM JJAS OND

JJASOND

400

Jinka
166 km²

400

Bilate
1980 km²

Q
P
E P 300 300

Moisture Zone

200

200

Hyper-arid
Arid
Semi-arid
Dry subhumid
Moist

100 100

0 0

JFMAM JJASOND JFMAM JJASOND

Figure 6.2. Regional differences in seasonality of precipitation (P), potential evaporation(E P ) and runoff (Q) across Ethiopia. Colours on the
map refer to aridity classes. Courtesy: Belete Berhanu.

et al., 1997 ; Cattanéo, 2005 ; Beechie et al., 2006 ; Monk
et al., 2006 , 2007 , 2008 ; Olden et al., 2006 ). The European
Water Framework Directive has formalised the need for
predictions of seasonal runoff variations within their river
water quality and ecosystem health assessment framework.
Seasonal runoff predictions in ungauged basins are also
needed to support decision making about water supply and
hydropower production (Niadas and Mentezelopoulos,
2008 ; Weingartner et al., 2012 ). Estimating natural flow
regimes in catchments where runoff is already modified by
human impacts is essential for planning restoration activ-
ities (e.g., Petts, 2007 ). The questions of when water is
available, how much water is available, and how reliably
these questions can be answered, are therefore key issues
for hydrologists concerned with environmental protection,
infrastructure

(hydrological year), which is termed the ' seasonal flow

regime for short (e.g., Harris et al.,

2000 ; Bower et al., 2004 ). However, the chapter will
discuss the variability of seasonal runoff between years
as well, since it has a significant bearing on the reliability
of water resources for various human and environmental
uses. The seasonal flow regime is a valuable indicator that
can be employed in comparative studies (Falkenmark and
Chapman, 1989 ) that classify and compare hydrological
signatures across regions, nations and continents. Figure
6.2 , for example, shows runoff, precipitation and potential
evaporation (E p ) regimes for several catchments in Ethi-
opia. The regimes indicate clear regional heterogeneity. In
the north of the country the flow regime has a single peak,
immediately following a single peak in precipitation. In
the south, there is little seasonality in runoff, and precipi-
tation is bimodal. Even without detailed knowledge of the
hydrology of Ethiopia, the flow regimes presented in
Figure 6.2 provide a basis for hypothesising the likely

' ,or ' flow regime '

development and water resources

management.
The focus of this chapter is on the mean seasonal
pattern of runoff variability over the annual cycle