.calculator-container {
font-family: Arial, sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 600px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-inputs, .calculator-results {
margin-bottom: 20px;
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 5px;
font-weight: bold;
}
.input-group input {
width: calc(100% – 12px);
padding: 8px;
border: 1px solid #ccc;
border-radius: 4px;
}
button {
background-color: #4CAF50;
color: white;
padding: 10px 15px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
width: 100%;
}
button:hover {
background-color: #45a049;
}
#result {
margin-top: 10px;
font-weight: bold;
text-align: center;
color: #333;
}
function calculateEvapotranspiration() {
var eto = parseFloat(document.getElementById("referenceEvapotranspiration").value);
var kc = parseFloat(document.getElementById("cropCoefficient").value);
var area = parseFloat(document.getElementById("area").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(eto) || isNaN(kc) || isNaN(area)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (eto < 0 || kc < 0 || area < 0) {
resultDiv.innerHTML = "Values cannot be negative.";
return;
}
// Actual Evapotranspiration (ETc) = ETo * Kc
var etc = eto * kc;
// Total Evapotranspiration Volume = ETc (mm/day) * Area (ha) * 10 (m³/ha/mm)
// Note: 1 mm over 1 hectare is 10 cubic meters (10,000 m² * 0.001 m)
var totalEvapotranspirationVolume = etc * area * 10;
resultDiv.innerHTML = "
Calculated Values:
" +
"Actual Evapotranspiration (ETc): " + etc.toFixed(2) + " mm/day" +
"Total Evapotranspiration Volume: " + totalEvapotranspirationVolume.toFixed(2) + " m³/day";
}
Understanding Evapotranspiration Rate
Evapotranspiration (ET) is the sum of evaporation from the land surface and vegetation, and transpiration from vegetation. It's a critical process in the water cycle, influencing soil moisture, crop yields, and water resource management.
* **Evaporation:** The process by which water changes from a liquid to a gas or vapor. In the context of ET, it refers to the direct loss of water from soil surfaces, water bodies, and wet plant surfaces.
* **Transpiration:** The process by which moisture is carried through plants from roots to small pores on the underside of leaves (stomata), where it changes to vapor and is released to the atmosphere.
Understanding and calculating ET is vital for various applications, including:
* **Agriculture:** Determining irrigation needs for crops, optimizing water use efficiency, and predicting crop yields.
* **Water Resource Management:** Assessing water availability in reservoirs, rivers, and groundwater systems.
* **Environmental Science:** Studying the impact of land use changes on local and regional water balances.
* **Meteorology:** Understanding atmospheric moisture content and its role in weather patterns.
### Key Components of the Calculation:
1. **Reference Evapotranspiration (ETo):** This is the rate of evapotranspiration from a hypothetical reference surface (usually well-watered grass) with a specific height and albedo. ETo represents the atmospheric demand for water and is influenced by climatic factors such as solar radiation, temperature, humidity, and wind speed. It is typically measured or calculated in millimeters per day (mm/day).
2. **Crop Coefficient (Kc):** This is a dimensionless factor that adjusts the reference evapotranspiration (ETo) to account for the specific water requirements of a particular crop or vegetation type. Different crops have different growth stages, canopy structures, and rooting depths, which affect their ET rates. Kc values vary throughout the growing season and are determined empirically or through modeling. A Kc of 1.0 means the crop's ET is equal to ETo, while values less than 1.0 indicate lower ET and values greater than 1.0 indicate higher ET.
3. **Actual Evapotranspiration (ETc):** This is the total amount of water lost from a specific crop or vegetation cover. It is calculated by multiplying the reference evapotranspiration (ETo) by the crop coefficient (Kc):
$$ ETc = ETo \times Kc $$
The result is also in millimeters per day (mm/day).
4. **Area:** The land area over which the evapotranspiration is occurring. This is typically measured in hectares (ha). 1 hectare = 10,000 square meters.
5. **Total Evapotranspiration Volume:** To understand the total water loss in terms of volume, the ETc rate is multiplied by the area. Since ETo and ETc are usually in mm/day, and we want the volume, we convert units. 1 mm of water over 1 hectare is equivalent to 10 cubic meters ($10,000 m^2 \times 0.001 m$). Therefore, the formula for total volume is:
$$ Total ET Volume (m^3/day) = ETc (mm/day) \times Area (ha) \times 10 (m^3/ha/mm) $$
This gives the total volume of water lost to the atmosphere per day from the specified area.
### Example Calculation:
Let's say we have a field of corn:
* **Reference Evapotranspiration (ETo):** 5.5 mm/day (This is the atmospheric demand based on weather data)
* **Crop Coefficient (Kc):** 0.75 (This value represents the corn's water use relative to ETo at its current growth stage)
* **Area:** 10 hectares
**Calculation:**
1. **Actual Evapotranspiration (ETc):**
$$ ETc = ETo \times Kc = 5.5 \text{ mm/day} \times 0.75 = 4.125 \text{ mm/day} $$
2. **Total Evapotranspiration Volume:**
$$ Total ET Volume = ETc \times Area \times 10 $$
$$ Total ET Volume = 4.125 \text{ mm/day} \times 10 \text{ ha} \times 10 \text{ m}^3/\text{ha/mm} $$
$$ Total ET Volume = 412.5 \text{ m}^3/\text{day} $$
In this example, the cornfield would lose approximately 4.125 mm of water per day from the surface and through transpiration, amounting to a total volume of 412.5 cubic meters of water lost per day. This information is crucial for planning irrigation schedules.