The Northern Pacific Slope
Costa Rica has 2 main seasons: the dry season, from December into May, and the rainy season, from May into December. Named by the Spanish colonialists who compared the seasons to their home Mediterranean climate, the dry season is referred to as verano (summer) and the rainy season, as invierno (winter). Depending on where you are in the country, the weather can vary dramatically by season. Costa Rica’s northern Pacific Slope—where Ensenada National Wildlife Refuge (NWR) and the Gulf of Nicoya are located—includes the land on the west side of the cordillera (mountain range) between the Nicaraguan border to the north and the Tárcoles River to the south. During the dry season, the Northern Pacific region experiences little to no rainfall. During the rainy season, though, this region receives plenty of rainfall—on average, about 5 feet of precipitation annually. (However, the southwestern Pacific slope generally receives 10 – 15 feet annually.)
This unusual climate has resulted in a unique ecosystem—the tropical dry forest. Costa Rica represents the southern boundary of this ecosystem in Central America. Half a millennium ago, tropical dry forest was the most abundant habitat in Central America, covering more than 200,000 square miles of the Pacific slope stretching from western Mexico to Panama. However, due to good soils and easy clearing, tropical dry forests have shrunk to less than 1% of their historical range. (Cutting the forest, then burning the remains, quickly transforms the land from forest to pasture lands. And the extended dry period helps to suppress weeds and pests.) In Costa Rica, most of the original dry forest has been converted to cattle pastures. Today, the tropical dry forest is considered the most threatened tropical forest habitat.
What is responsible for this unusual ecosystem? In effect, the lands of the Pacific slope are in the rain shadow of the mountains. During the dry season, the strong alisios (trade winds) from the northeast carry moist Caribbean air inland. Hitting the cordilleras (which stretch the length of the country), this air rises and cools. Since colder air can’t hold as much moisture as warmer air, the air drops the moisture on the Caribbean flank. Thus, by the time the air gets over the mountains and onto the Pacific slope, it is dry. During the rainy season, though, the alisios weaken, allowing weather patterns to bring moisture into the north slope lands directly from the Pacific. Hence, 5 feet of rain during that period.
But why does the northern Pacific slope experience this dry season while the southwestern Pacific does not? The northern mountains are lower, with more gradual slopes that create a smooth flow of dry, downsloping air. As a result, the area experiences day after day of strong sun, cloudless skies, and no precipitation. The mountains in the south, though, are higher with steeper inclines, creating a disturbed flow of air. As a result, a swirl or vortex is created on the Pacific side of the mountains there, which scoops in moisture-laden air from the Pacific into the southwestern Pacific slope area.
Trees in the dry forest are adapted to survive these periodic drought conditions. For example, many dry-forest trees drop their leaves during the dry season to conserve water. At the same time, many burst into flower to take advantage of the constant winds during this season to disperse pollen and seeds. As a result, the trees paint an interesting backdrop of leafless branches crowned by soft colors—for instance, the oaks have pink flowers; the guanacaste, laurel, and ceiba, white flowers.
We stayed both nights at Hacienda La Ensenada (ensenada means “cove”), in lovely cabinas looking out on the Gulf of Nicoya and the mountains of the Nicoya Peninsula in the distance. La Ensenada is located in a 1200-acre national wildlife refuge, established in 1998, made up of a family-run cattle finca (ranch) with nature trails and a lake. A salina (salt production facility) on the property floods ponds to harvest 1300 bags of salt a week during the dry season.
Click here to read details of our stay in this area—first, Hacienda La Ensenada and Ensenada NWR.