Human impacts on the hydrology of the
páramos
Since the 20th century, the páramos have been facing unprecedented
anthropogenic pressures (Molina et al., 2015; Roa-García et al., 2011;
White, 2013). There is increasing evidence that anthropogenic activities
such as intensive and extensive livestock (Molina et al., 2007),
cultivation and land management practices affect negatively the páramos’
local biodiversity, their functional capacity (Erwin, 2009) and total
water yield (Buytaert et al., 2007a). Scientific and public awareness
raised concerning the lack of knowledge about the potential impact of
rural development and ecosystem degradation on the hydrology of páramos
(Célleri and Feyen, 2009).
Research focused in anthropogenic intervention impacts on hydrological
services of páramos (Buytaert et al., 2007b), explored the shift from
endemic land cover to cultivation lands, livestock and forest
plantations, anthropic introduction of fire and degradation (Poulenard
et al., 2001).
Cultivation tends to reduce the catchment regulation capacity (⁓40%
reduction) (Célleri and Feyen, 2009; Ochoa-Tocachi et al., 2016a)
increases peak discharge (⁓20%), reduces base flow (⁓50%) (Buytaert et
al., 2006a, 2007a) and reduces the soil storage capacity (up to 26%
reduction) (Sarmiento, 2000). Cultivation also reduces the soil field
capacity (from 100% to 83%) and wilting point (from 83% to 63%)
(Díaz and Paz, 2002), and the increase of evapotranspiration rates (up
to 66%) (Sarmiento, 2000).
Livestock density tends to increase, with often negative impacts on the
soil structure. Díaz & Paz, (2002) report an increase of the soil bulk
density up to 0.2 g cm3 under extensive and 0.7 g
cm3 under intensive conditions compared to undisturbed
páramo soils in Popayán Colombia. Water yield reduction as a result of
increasing evaporation is typically less than 15% (Crespo et al.,
2010), but this tends to be accompanied by an increase in streamflow
flashiness and a decrease in hydrological regulation capacity
(Ochoa-Tocachi et al., 2016a, 2016a).
The introduction of exotic species as a forestation strategy has been a
common practice in the Andean páramos. Pine trees in particular have
been used as a strategy to improve the inhabitants’ income (Farley et
al., 2004) but may affect the hydrological response of páramo
ecosystems. Pairwise catchment experiments in southern Ecuador showed
that base flow reduced up to 66% (Buytaert et al., 2007b; Ochoa-Tocachi
et al., 2016a), water yield decreases between 42% to 50% (Crespo et
al., 2010; Ochoa-Tocachi et al., 2016a) as consequence of interception
in the canopy and higher evapotranspiration. Burning, another common
practice increases the soil erosion, the amount of runoff, reduces the
rainfall-runoff time response (Molina et al., 2007), as well as the
saturated soil hydraulic conductivity (Poulenard et al., 2001). Drying
and hydrophobicity up to 40% have been reported due the direct exposure
of dark soils to sunshine (Buytaert et al., 2002). However, a recent
study shows that programs aimed at the conservation of hydrological
services and soil maintenance do not necessarily need to exclude burning
to assure adequate long-term vegetation cover in disturbed páramos
(Bremer et al., 2019).
Climate change impacts on
páramos
Climate change is very likely to have an impact on the páramos and their
ecosystem services. Global warming effects on temperature are generally
well quantified with agreement amongst models on the direction of
change. This is due to both a higher air moisture content resulting from
increased evapotranspiration and the intensification of the Hadley
circulation in tropical regions. Both processes are expected to lead to
increased temperatures at high altitude (Bradley et al., 2009). However,
precipitation and subsequent discharge variations are much more variable
with differences up to 50% between various Intergovernmental Panel on
Climate Change (IPCC) models from the currently observed values in the
Andes (Buytaert and De Bièvre, 2012). For instance, González-Zeas et al.
(2019) compared results from a Regional Climate Model (RCM) with
observed data in a catchment that provides 30% of the water needs of
Quito, the capital of Ecuador. They found considerable disagreement
between both data sources with an over prediction of precipitation by
the RCM. In addition, major spatial differences exist, in spite of all
the uncertainties across climate projections. Whereas part of the
Bolivian Altiplano is likely to experience a reduction of 10%
precipitation, areas of the Peruvian Andes will potentially be subjected
to increases up to 60% (Buytaert and De Bièvre, 2012). Exacerbating the
underlying climate is the El Niño Southern Oscillation (ENSO), an
imbalance of sea-surface temperatures (SST) and ensuing air pressure in
the tropical Pacific (NOAA, 2019). This phenomenon has severe impacts
over global and, Andean and Central America weather. El Niño events,
where SST anomalies are positive, lead to increased drought risks across
the Bolivian Altiplano combined with intense precipitation over northern
Peru and Ecuador. Conversely, during a La Niña, where SST anomalies are
negative, an intensification of precipitation is observed causing major
flooding in certain areas of the tropical Andes (Zolá and Bengtsson,
2006). (Mendoza et al., 2019) proposed intra- and inter-annual scale
climate teleconnections with Trans Niño Index (TNI), North Athlantic
Oscillation (NAO) and the Caribbean Index (CAR). Additionally, the
altitudinal factor plays an important role, when the westerly winds
dominate, dry conditions occur especially at high altitude, while the
opposite when the easterly winds dominate. In this case all the moisture
from the eastern Pacific Ocean is transferred to the mountain range.
ENSO occurs naturally and is not a consequence of climate change.
However, the intensity and duration of ENSO events has increased
substantially in the last decades, indicating a possible link to
anthropogenic-induced climatic changes that occurred in the same period.
These changes will propagate through the terrestrial water cycle, thus
affecting directly its hydrology. Studies have quantified these changes,
Wouter Buytaert & De Bièvre (2012) showed that most of the northern
Andean region is expected to experience an increase in precipitation.
However, the increase in evapotranspiration as a result of warming is
likely to compensate the increase in precipitation, resulting in a net
reduction in effective precipitation and water availability.
Climatic changes will affect ecosystems more broadly through changes in
vegetation and soils, which may propagate to the water cycle. In
mountain regions, climate change is likely to induce shifts in the
distribution of ecosystems and biomes. Logistic regressions coupled with
Global climate models (GCM) and Climate Networks (CN) have been used to
simulate climate patterns in future scenarios and to estimate the extent
of such future changes for the tropical Andes ((Tovar et al., 2013a;
Vázquez‐Patiño et al., 2020). Tovar, Arnillas, et al. (2013) estimated
that the páramos may lose 30% of their current areas due to a lack of
room for upslope migration, necessary in the face of warmer temperatures
at higher elevations. Additionally, species distribution is also at risk
(Ramirez-Villegas et al., 2014). More than 50% of species considered
could experience reductions in quantities up to 45% with 10%
potentially extinct.
However, despite these advances, estimating changes in mountainous areas
remains inherently difficult, making the downscaling of global or
regional coarse resolution models highly uncertain as the highly
variable topography results in steep and sudden changes in local weather
patterns which are difficult to represent in available GCMs (Buytaert et
al., 2010). Moreover, simplifications of climate processes and errors in
input data exacerbate the problem. As we subsequently discuss, new tools
such as citizen science and participatory monitoring, provided
agreed-upon data quality and reliability standards, can help bridge some
of those hydrometeorological information gaps.
In the midst of a highly unpredictable future, water and land
decision-makers will have to resort to various methods of incorporating
uncertainty in increasing resilience in the face of climate shocks, from
scenario analysis in designing infrastructure to implementing measures
to control growth on the demand side.