286
Climatic Geomorphology
floods (such as that of the 28th July, 1990, which developed a delta at the mouth of the
lower Huerva River, a tributary of the Ebro in Spain.
Precipitation in arid regions varies significantly (Figure 10.4) and, as a result, greatly
influences changes in run-off and sediment production. For example, in the middle of the
Ebro Depression, at an experimental station for studying run-off and erosion at Lanaja
in Huesca Province, Spain (Figure 13.1), a 4-year record shows that the most important
precipitation corresponds to convective storms that occur primarily during spring and
autumn, with some in summer. The rest of the rainfall is from convective cells and is of
low magnitude (Guti~rrez et al., 1995). For this reason, the highest values of run-off and
erosion take place in spring and autumn. Intensities vary considerably within convective
cell precipitation. At times, the recorded rainfall from one storm exceeds the total mean
annual precipitation. Furthermore, experimental stations with a large quantity of rain
gauges show sharp spatial variations and steep gradients (Figure 13.2).
In the literature, a number of cases are cited where precipitation is related to the
advection of humid air masses supplying continuous rainfall to a semi-arid region (Inbar,
1972; in Starkel, 1976). The Mediterranean winter rainfall that reaches the mountains of
Lebanon, Israel, and Syria is an example. Rainfall during a 4-day period (20th to 23rd
January, 1969) varied between 120 and 360 mm, equivalent to a third of the mean annual
precipitation. Despite the low mean intensities of 2 to 3 mm/h, occasionally exceeding
8 mm/h, this rainfall corresponded to a return period of 100 years. During this event,
0.04 mm/yr of downcutting, six times the normal rate, was produced in the upper
Meshushim basin. This shows that storm precipitation can be of considerable importance
in semi-arid regions.
60
55
50
45
4O
E
E 35,
30
.=_
rr
25
20
15,
10,
Summe(
If. It[ l Jll Jl
[Autumn ! Winter I Spring lSummer ! Autumn i Winter I Sprin~ i SummerJAutumn I Winter ! Spring
1991
'
1992
'
I
1993
l
1994
Figure 13.1. Precipitation record at the Lanaja Experimental Station in Huesca Province, Spain, for the
period July 1991 to May 1994 (Guti~rrez et al., 1985).
Climatic Geomorphology
floods (such as that of the 28th July, 1990, which developed a delta at the mouth of the
lower Huerva River, a tributary of the Ebro in Spain.
Precipitation in arid regions varies significantly (Figure 10.4) and, as a result, greatly
influences changes in run-off and sediment production. For example, in the middle of the
Ebro Depression, at an experimental station for studying run-off and erosion at Lanaja
in Huesca Province, Spain (Figure 13.1), a 4-year record shows that the most important
precipitation corresponds to convective storms that occur primarily during spring and
autumn, with some in summer. The rest of the rainfall is from convective cells and is of
low magnitude (Guti~rrez et al., 1995). For this reason, the highest values of run-off and
erosion take place in spring and autumn. Intensities vary considerably within convective
cell precipitation. At times, the recorded rainfall from one storm exceeds the total mean
annual precipitation. Furthermore, experimental stations with a large quantity of rain
gauges show sharp spatial variations and steep gradients (Figure 13.2).
In the literature, a number of cases are cited where precipitation is related to the
advection of humid air masses supplying continuous rainfall to a semi-arid region (Inbar,
1972; in Starkel, 1976). The Mediterranean winter rainfall that reaches the mountains of
Lebanon, Israel, and Syria is an example. Rainfall during a 4-day period (20th to 23rd
January, 1969) varied between 120 and 360 mm, equivalent to a third of the mean annual
precipitation. Despite the low mean intensities of 2 to 3 mm/h, occasionally exceeding
8 mm/h, this rainfall corresponded to a return period of 100 years. During this event,
0.04 mm/yr of downcutting, six times the normal rate, was produced in the upper
Meshushim basin. This shows that storm precipitation can be of considerable importance
in semi-arid regions.
60
55
50
45
4O
E
E 35,
30
.=_
rr
25
20
15,
10,
Summe(
If. It[ l Jll Jl
[Autumn ! Winter I Spring lSummer ! Autumn i Winter I Sprin~ i SummerJAutumn I Winter ! Spring
1991
'
1992
'
I
1993
l
1994
Figure 13.1. Precipitation record at the Lanaja Experimental Station in Huesca Province, Spain, for the
period July 1991 to May 1994 (Guti~rrez et al., 1985).