An increase in the water level in a rain gauge after 1 hour is shown in Fig. 1.
Find the percentage increase in the water level.
Answers
Answer:
A rain gauge is a meteorological instrument to measure the precipitating rain in a given amount of time per unit area. The instrument consists of a collection container which is placed in an open area. The precipitation is measured in terms of the height of the precipitated water accumulated in the container per given time and is expressed in millimetres. Since the same amount of rain precipitation is assumed to be occurring around the container, the area of collection is not a factor. However, it should not be too small, neither should it be too large. Due to spatial uniformity of rainfall, 1 mm of measured precipitation is the equivalent of 1 L of precipitated rain water volume per metre squared.
A tipping bucket rain gauge consists of a pair of rainwater collecting buckets. It is covered by a funnel, with an open collector area at the top where A is the area of collection. The buckets are so placed on a pivot that only one bucket remains under the funnel at a time. During rain, rain water is collected in the collecting bucket, through the funnel. When the water fills up to a known point of the bucket, say having a volume v, the bucket tips, emptying the water. When one bucket tips, the other bucket quickly moves into place to collect rainwater. Each time a bucket tips, an electronic signal is sent to a recorder which is registered by the instrument with time stamp.
To calculate the total rainfall in a given interval, the total number of tips occurring in the interval is observed. If this number be ‘N’, then in that time the total volume of water collected is N × v, where v is the volume of the bucket necessary to be filled for tipping. Now, if A be the area of collection of the rain at the funnel top, then the total rain amount RA, occurring in the given time in terms of height is
(7.2)
Therefore, the least count of the instrument is k = v/A which is the rainfall measured for a single tip. The same arrangement may also be used to calculate the rain rate. If two subsequent tips have occurred in an interval δt, and N × k mm of total rain has occurred in this time δt, then the rain rate occurring in this instant is
(7.3a)
To express the rain rate in the standard form of mm/h, the following expression can hence be used
(7.3b)
where k is in mm and is given by k = v/A × 10− 3, where v is in cubic centimeter (cc) and the area is in metre squared. δt is in second.
The tipping bucket rain gauge is especially good at measuring drizzle and light rainfall events. The resolution is better when the least count k is small and the clock measuring δt is precise. However, the least count cannot be made arbitrarily small, as for such case there will be many tips of the bucket during heavy rain that some of the rain will go uncollected during the bucket transition leading to an underestimate of the rainfall and inaccuracy