42
E. A. Agosta et al.
Climatic Factors and Floods
Precipitation Trends in Present Climate
The spatial flood risk structure from Fig. 3 is consistent with the spatial mean annual
precipitation distribution (compare with Fig. 2), especially over the plains of eastern
Argentina, east of the Andes. The region denotes both large annual mean total precipitation values and high values of structural flood risk. Therefore, changes in mean
precipitation and strong localized rainfalls can significantly contribute to flooding
variations, which in turn may alter the mapping of flood risks.
Estimated from meteorological station data (Fig. 1, panel b), the mean annual total
precipitation (ATOTP) and the associated precipitation change due to linear trends in
the period 1961–2015 are shown in Fig. 5, panels a and b, respectively. Overall, the
precipitation changes are positive over most ESA territory. As a regional average,
ESA rains about 150 mm more precipitation over the period 1961–2015, i.e., about
15% of the regional average. The precipitation rises over 500 mm (about 30% of the
local historical average) in the northeastern portion of ESA, in the Misiones Province.
Note that this northern territory of ESA matches a fraction of the main catchment
area of the upper Paraná; thereby, this precipitation increase is influencing the river
runoff. Rainfalls also rise in central and southeastern ESA, with increases about 20–
25% of the local historical averages (i.e., increases between roughly 150 mm in the
central ESA and 250 mm to the east and along the western bank of the Río de la
Plata estuary). In the GBA subregion, annual mean total precipitation has increased
about 200 mm on average (i.e., about 20% of the historical average).
Several studies have documented that daily extreme rainfalls have substantially
increased during the twentieth century in southeastern South America (Cavalcanti
et al. 2015, and references therein) and Argentina (Penalba and Robledo 2010),
mostly attributable to climate change. To assess the impact of extreme precipitation
changes in the region, we examine linear changes of the total annual precipitation
due to strong precipitation days (R75p95pTOT; Fig. 5, panels c and d) and extreme
precipitation days (R95pTOT; Fig. 5, panels e and f) over the period 1961–2015. The
daily precipitation extremes show positive changes over most areas of ESA region,
though with sharp local variations (Fig. 5, panels c–f). The spatial distribution of
change is like that of the annual total precipitation changes. Strong positive changes
are observed over the Misiones Province and along the western shore of the Rio de
la Plata estuary, in which GBA is settled. The total annual precipitation due to days
with strong precipitation has increased about 90 mm on average over ESA, which
represents about 20% of the historical total precipitation due to strong precipitation.
The average increase over GBA subregion is about 140 mm, equivalent to over 30%
of the historical total precipitation due to strong precipitation, changes comparable
to those observed in northeastern ESA.
On a decadal perspective, positive trends in extreme precipitation indices are
predominant from the 1960s. Figure 6 shows the decadal mean of annual precipitation totals due to strong precipitation days (R75p95pTOT). Note that discriminating
E. A. Agosta et al.
Climatic Factors and Floods
Precipitation Trends in Present Climate
The spatial flood risk structure from Fig. 3 is consistent with the spatial mean annual
precipitation distribution (compare with Fig. 2), especially over the plains of eastern
Argentina, east of the Andes. The region denotes both large annual mean total precipitation values and high values of structural flood risk. Therefore, changes in mean
precipitation and strong localized rainfalls can significantly contribute to flooding
variations, which in turn may alter the mapping of flood risks.
Estimated from meteorological station data (Fig. 1, panel b), the mean annual total
precipitation (ATOTP) and the associated precipitation change due to linear trends in
the period 1961–2015 are shown in Fig. 5, panels a and b, respectively. Overall, the
precipitation changes are positive over most ESA territory. As a regional average,
ESA rains about 150 mm more precipitation over the period 1961–2015, i.e., about
15% of the regional average. The precipitation rises over 500 mm (about 30% of the
local historical average) in the northeastern portion of ESA, in the Misiones Province.
Note that this northern territory of ESA matches a fraction of the main catchment
area of the upper Paraná; thereby, this precipitation increase is influencing the river
runoff. Rainfalls also rise in central and southeastern ESA, with increases about 20–
25% of the local historical averages (i.e., increases between roughly 150 mm in the
central ESA and 250 mm to the east and along the western bank of the Río de la
Plata estuary). In the GBA subregion, annual mean total precipitation has increased
about 200 mm on average (i.e., about 20% of the historical average).
Several studies have documented that daily extreme rainfalls have substantially
increased during the twentieth century in southeastern South America (Cavalcanti
et al. 2015, and references therein) and Argentina (Penalba and Robledo 2010),
mostly attributable to climate change. To assess the impact of extreme precipitation
changes in the region, we examine linear changes of the total annual precipitation
due to strong precipitation days (R75p95pTOT; Fig. 5, panels c and d) and extreme
precipitation days (R95pTOT; Fig. 5, panels e and f) over the period 1961–2015. The
daily precipitation extremes show positive changes over most areas of ESA region,
though with sharp local variations (Fig. 5, panels c–f). The spatial distribution of
change is like that of the annual total precipitation changes. Strong positive changes
are observed over the Misiones Province and along the western shore of the Rio de
la Plata estuary, in which GBA is settled. The total annual precipitation due to days
with strong precipitation has increased about 90 mm on average over ESA, which
represents about 20% of the historical total precipitation due to strong precipitation.
The average increase over GBA subregion is about 140 mm, equivalent to over 30%
of the historical total precipitation due to strong precipitation, changes comparable
to those observed in northeastern ESA.
On a decadal perspective, positive trends in extreme precipitation indices are
predominant from the 1960s. Figure 6 shows the decadal mean of annual precipitation totals due to strong precipitation days (R75p95pTOT). Note that discriminating