The question of whether Bakersfield, California, is a desert requires moving beyond common perception and applying the strict scientific definitions used by climatologists worldwide. Answering this query involves using established systems that categorize climates based on specific, measurable data points. This provides a definitive framework for understanding the region’s unique environment.
Scientific Criteria for Desert Classification
Climates are systematically classified using metrics that measure the long-term balance between water supply and water demand. The most widely accepted system for dry regions is the Köppen-Geiger classification, which groups arid and semi-arid regions into the “B” group. This system fundamentally distinguishes a dry climate based on whether precipitation can meet the atmospheric demand for moisture.
The core concept for defining aridity is the relationship between precipitation (P) and potential evapotranspiration (PET). PET is the maximum amount of water that could evaporate from the land surface and transpire from plants. A true desert, or arid climate (designated BW), is a region where the moisture deficit is substantial and permanent. These areas receive very little rainfall, often below 10 inches (250 millimeters) annually, combined with very high evaporation rates.
A semi-arid climate (designated BS) is slightly less dry than a true desert. These regions receive enough precipitation to support sparse grasses and shrubs, but not enough to sustain forests or dense vegetation. The mathematical threshold for classifying a climate as arid versus semi-arid is complex. It involves formulas that factor in mean annual temperature and the seasonal distribution of rainfall to accurately reflect local water stress.
Bakersfield’s Official Climate Zone
Applying these scientific metrics, Bakersfield is officially classified under the Köppen-Geiger system as having a BWh climate, which stands for a Hot Desert Climate. While often colloquially referred to as semi-arid, long-term meteorological data pushes the region into the true desert category, confirming a permanent and significant moisture deficit.
The average annual precipitation in Bakersfield is low, measuring between 6.5 and 7 inches (165 to 178 millimeters). This measurement falls below the general 10-inch threshold often used to delineate the boundary between semi-arid and arid zones. Furthermore, precipitation is highly seasonal, with the summer months of June through September often recording less than one-tenth of an inch of rain combined.
The “h” in the BWh designation signifies a hot climate, characterized by scorching summers. Bakersfield regularly experiences extreme heat, with high temperatures reaching or exceeding 90°F for an average of over 100 days a year. The city records more than a month’s worth of days where the temperature climbs above 100°F. This combination of extremely high temperatures and very low precipitation results in an exceptionally high potential evapotranspiration.
Geographic Factors Driving Bakersfield’s Aridity
The primary reason for Bakersfield’s desert-like conditions is its location within the San Joaquin Valley, heavily influenced by the rain shadow effect. The city sits on the valley floor, bordered to the east by the towering Sierra Nevada mountain range. These mountains act as a massive barrier to moisture-laden air moving inland from the Pacific Ocean.
As the prevailing winds push the moist air up the western slopes of the Sierra Nevada, the air cools and condenses. This causes nearly all of its moisture to fall as rain or snow on the western slopes in a process called orographic lift. By the time the air passes over the mountain crests and descends toward the valley floor, it has been stripped of its water content.
This descending air then warms adiabatically, which lowers its relative humidity and increases its capacity to hold any remaining moisture. Consequently, the air mass dries the land below, creating the rain shadow effect responsible for Bakersfield’s aridity. This geographical positioning, with the valley surrounded by mountains on three sides, severely limits maritime influence and locks the region into its characteristically dry climate.