Introduction

Ecuador is endowed by Nature with unmatched ecological diversity. This is due to: (1) its geographical location along the Equator, (2) its relative continental position next to the Pacific Ocean, and (3) the presence of the Andes Mountain Range, which crosses the middle of the country from North to South (Figure 1). This unusual combination of near-zero latitude, proximity to a very large moisture source, and wide altitudinal range is responsible for a substantial ecological and biological diversity. Therefore, the region constitutes a veritable field laboratory for the study of tropical ecological, hydrological, and climatological relations.

Figure 1 Map of Ecuador, showing Andes Mountain Range passing through the middle. 

The general objectives include describing the uniqueness of the chosen study region and its climatological and geomorphological characteristics, with aim to establish the appropriate foundations for the nascent field of ecohydroclimatology, interpreted as the seamless approach to ecology, hydrology, and climatology. Specific objectives include the description of mean annual precipitation, terrain geology and geomorphology, relation of flora to distance to groundwater, and appropriate climatic indicators such as the various bioclimatological indexes.

This study focuses on the southern provinces of Loja and Zamora-Chinchipe (Figure 1). These regions feature marked gradients in mean annual precipitation within a relatively short distance. Figure 2 shows mean annual precipitation in Loja and Zamora-Chinchipe, varying between 200-400 mm in Loja to 32006400 mm in Zamora-Chinchipe. Thus, a transect of relatively limited length transversing these two provinces is appropriate for the study of ecohydroclimatological relations.

Figure 2 Mean annual precipitation in Ecuador. 

This study is part of a research program in ecohydroclimatology carried out jointly by San Diego State University (San Diego, California, USA) and the Universidad Tecnica Particular de Loja (Loja, Ecuador).

Geographical Setting

The provinces of Loja and Zamora are located in southern Ecuador. ^{Wolf (1892)} has described the geology, geomorphology, and hydrography of Ecuador, including Loja and Zamora. The Andes Mountain Range transverses the study region, from the Sabanilla Knot, to the south of Loja, to the moorlands of Saraguro, toward the north.

From the Sabanilla Knot, the Santa Rosa Range takes off to the northwest and the Condor Range to the southeast. The Santa Rosa Range is narrow, low, and relatively small. From the Condor Range, several large branches take off toward the northeast.

From 4° 8' S latitude, south of the city of Loja, the Western Range runs parallel to the Eastern Range in a general northern direction. The Western Range is narrow, with short branches on both sides, rising up to 3000 m through most of its length. In contrast, the Eastern Range rises up to 4000 m. These two branches of the Andes are united by two transversal knots, the Cajanuma Knot to the south of Loja, and the Guagrauma Knot to the north. The region comprised between the knots constitutes the valley of Loja.

The valley of Loja, oriented from north to south, is divided into two different sections. The northern section is narrow, resembling a canyon. The southern section, properly the valley of Loja, is oval-shaped, with a total length comprising about 6 km and a maximum width of about 3 km.

The Malacatos River has its headwaters in the Cajanuma Knot, flowing north to meet the Zamora river at Loja proper, where it takes the name of the latter. Continuing to flow north through the Guagrauma Knot, the Zamora river meets several tributaries along its course, eventually discharging into the Santiago river in the eastern lowlands of Zamora-Chinchipe province.

The interandean valley of Loja is small and low, at 2150 m altitud, with the city of Loja occupying the entire valley. The lowest point on the road (pass) from Loja through Cajanuma Knot to the south is at 2525 m altitude. The lowest point on the road from Loja to Catamayo to the west is at 2786 m. This pass is next to Villonaco peak, which rises to about 3000 (^{Wolf, 1892}).

Conceptual Framework

This study sets the foundations to describe the characteristics of vegetative communities, using the interdisciplinary perspective of ecohydroclimatology. Several factors condition the type and density of vegetative communities across the landscape. The most important are:

Seasonal Variations in Temperature

Plants are naturally adapted to seasonal variations in temperature, which are conditioned by latitude, altitude, and continental location relative to the nearest moisture source. Desert plants readily adapt to wide variations in seasonal temperature, while rainforest plants do not.

Annual Precipitation

The transect chosen for this study comprises the section between Catacocha, in central Loja province, to Zamora, in western Zamora-Chinchipe (Figure 3).

Figure 3 General location of the study transect in the Loja and Zamora-Chinchipe provinces. 

Figure 4 shows a map of mean annual precipitation for the study transect. Data from ten (10) climatological stations were used to develop this map. The stations are, from west to east: (1) Chaguarpamba, (2) Catacocha, (3) Nambacola, (4) El Cisne, (5) Catamayo, (6) El Tambo, (7) La Argelia (in Loja), (8) Cajanuma, (9) San Francisco, and (10) Zamora. The locations of the stations are shown in Figure 4.

Figure 4 Mean annual precipitation isohyets for the Catacocha-Zamora transect. 

Mean annual precipitation varies from 400 mm in Catamayo to 2200 mm in San Francisco, depicting a marked precipitation gradient. The straight distance between Catamayo and San Francisco is about 40 km, while the straight distance between Catacocha and Zamora is about 80 km. Significantly, the city of Loja, capital of the province of Loja, is located at midrange along the Catamayo-San Francisco subtransect.

Figure 5 shows an image of the Catacocha-Zamora transect, revealing the marked diferences in vegetation along the transect. Albedo, a reliable indicator of the presence or absence of vegetation is estimated to vary between as high as 0.30 near Catamayo, to as low as 0.05 near San Francisco (^{Ponce, Lohani, & Huston, 1997}). Figure 6 shows a longitudinal profile of the Catacocha-Zamora transect, corresponding to Figure 5. The Catacocha, Catamayo, Loja, and Zamora valleys are indicated in the profile.

Figure 5 Topographic map comprising the Catacocha-Zamora transect. 

Figure 6 Longitudinal profile of Catacocha-Zamora transect. 

Figure 7 shows an image of the Catamayo-Zamora transect, at somewhat larger scale that the previous image, again revealing the marked diferences in vegetation type and density along the transect. ^{Pulgar, Izco and Jadan (2010)} have noted that mean annual precipitation at an isolated spot at Cerro El Consuelo, near San Francisco, has been measured at 6 259 mm. Also, they have documented the number of rainy months to vary from 1-2 for Catamayo (a hyperarid climate) to 11-12 for San Francisco (a hyperhumid climate) (^{Ponce, Pandey, & Ercan, 2000}). Thus, the Catamayo-San Francisco subtransect appears to be optimal for the study of tropical ecohydroclimatological relations.

Figure 7 Image of the Catamayo-Zamora transect. 

Figure 7 shows an image focused on the Loja valley, showing the marked differences in vegetation density from the mountains west of Loja to those east of Loja, a distance of less than 20 km. Mean annual precipitation (Figure 8) varies from 800-1000 mm to the west and 1600-1800 mm to the east.

Figure 8 Mountainous semiarid landscape in the vicinity of Catamayo, Loja province. 

Vegetative Landscapes

Figures 8 and 9 show the contrast between typical landscapes and associated vegetative communities in Catamayo and Zamora, respectively. Figure 8 shows a hilly landscape covered with short semiarid shrubs and grasses, while Figure 9 shows a dense tropical montane humid forest, featuring relatively tall trees. Ongoing field research is aimed at identifying the spatial distribution, density, size, and other relevant characteristics of vegetative species and communities along the study transect.

Figure 9 Vegetative communities along the road to Zamora, Zamora-Chinchipe province. 

Bioclimatological Indexes

Three indexes are used to study bioclimatological relations (^{Rivas-Martínez 2007}):

Continentality index

This index is equal to the average temperature of the hottest month T_hot minus the average temperature of the coldest month T_cold .

1

The following procedure is used to calculate T_hot :

The maximum daily temperature, for each month and year of record is identified, and the mean maximum monthly temperature is calculated.

The mean of the mean maximum monthly temperature is calculated for the entire record.

The month with the highest mean of the mean maximum monthly temperature is selected as the hottest month.

A similar procedure is applied to calculate T_cold .

The continentality index varies between I_c = 0 for an extreme oceanic influence, to I_c = 65 for an extreme continental influence.

Thermicity index

This index is equal to the mean annual temperature T_mean plus the mean of the monthly mean minimum temperatures T_min plus the mean of the monthly maximum temperatures T_max . The sum is multiplied by 10.

2

The mean annual temperature is the mean of the (12) mean monthly average temperatures. The mean of the monthly minimum temperatures in the mean of the (12) mean monthly minimum temperatures. The mean of the monthly maximum temperatures in the mean of the (12) mean monthly maximum temperatures.

Positive Temperature Index

This index is equal to the sum of all positive (nonnegative) mean monthly temperatures. The sum is multiplied by 10.

3

Table 1 shows the classification of climates as a function of the continentality index. Table 2 shows the classification of climates as a function of the thermicity and positive temperature indexes. Table 3 shows the indexes calculated for the following stations: (1) Catacocha, (2) Catamayo, (3) La Argelia, and (4) Zamora. Table 4 shows the climatic classification for the stations considered in this study.

Table 1 Classification of climates based on continentality index. 

Table 2 Classification of climates based on thermicity and positive temperature indexes. 

Table 3 Bioclimatological indexes for stations in the study region. 

Table 4 Classification of stations based on bioclimatological indexes. 

The low continentality index of the stations along the study transect justifies its classification ashyperoceanic (Table 1). This is attributed primarily to its geographical location near the Equator, and secondarily to its near proximity to the Pacific Ocean.

Summary

Ongoing ecohydroclimatological research along the Catacocha-Zamora transect in the provinces of Loja and Zamora-Chinchipe, Ecuador, is reported. Mean annual precipitation varies between 400 mm in Catamayo, along the study transect, to 2200 mm in Zamora, toward the eastern limit. Precipitation data indicates that mean annual precipitation may reach 6259 mm in an isolated point at Cerro del Consuelo, in the Podocarpus National Park, near Loja. Altitudinal variations are also quite marked, between 1230 m in Catamayo, to 2930 m in Cerro del Consuelo, to 900 m in Zamora. Ecohydrological and hydroclimatological data are examined with the aim of underpinning research in the nascent field of ecohydroclimatology.